Meatless Monday Challenge

Creamy Twice-Baked Mashed Potatoes (Great for Leftovers!)

on October 17, 2023
last updated November 28, 2023
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These Twice Baked Mashed Potatoes are a Marley's Menu Instagram community favorite! This recipe takes creamy mashed potatoes and bakes them with cheese and green onions for the ultimate potato side dish. You will learn how to make this dish both from scratch or by utilizing leftover mashed potatoes.
Twice Baked Mashed Potato Casserole with Scallions

Want to uplevel your potato side dish? These Creamy Twice-Baked Mashed Potatoes are decadent, comforting, cheesy, and packed with flavor. Plus, you can make this casserole from scratch, or use this recipe to use up leftover mashed potatoes.

Think velvety mashed potatoes, loaded with cheese and scallions, baked to golden perfection with a crispy cheddar top layer. It’s one of those indulgent potato dishes that warms your soul and brings comfort to your dinner plate.

Despite the casserole’s nomenclature, russet or Yukon gold potatoes are first boiled, then baked, for the best textures and flavors you can possibly create out of a humble potato.

Cheesy Twice-Baked Mashed Potato Casserole with two serving spoons.

As an environmental scientist, reducing my food waste is a top priority for me! Which means finding clever ways to reinvent leftovers is definitely in my wheelhouse!

This casserole answers the question: “what should I do with my leftover mashed potatoes?” and turns them into a dish that certainly doesn’t taste like an afterthought.

Green tip: Of the billions of tons of food wasted annually, 50% of food waste happens at home. Reduce your contribution to food waste by properly storing, reheating, and consuming leftovers.

Twice-Baked Mashed Potatoes Ingredients & Substitutions

Here’s everything you need to make these from scratch:

  • Russet or Yukon gold potatoes. I tested this recipe with both russet and Yukon gold potatoes and it works beautifully with both. I tend to use russet just because I grew up on russet mashed potatoes, so it feels more natural for my cooking. Both were creamy, tender, and buttery.
  • Milk. This recipe works with any dairy milk from skim to whole or even heavy cream. It also works with any unsweetened, unflavored non-dairy milk.
  • Unsalted butter. This recipe calls for unsalted butter because both the garlic salt and cheddar cheese bring plenty of salt to this dish. Using salted butter may send your potatoes over the edge into too-salty territory. However, if you only have salted butter on hand, you can use that and substitute the garlic salt for garlic powder.
  • Garlic salt. I love using garlic salt in my mashed potatoes because it simultaneously salts them and adds a garlicky flavor. If you don’t have garlic salt on hand, you can substitute 1/2 teaspoon salt and 1/2 teaspoon garlic powder.
  • Black pepper.
  • Cream cheese. You can use reduced fat or full fat dairy cream cheese, or even a nondairy substitute. My preference is to use light cream cheese in this recipe but use whatever you have in your fridge or whatever you like to cook with. Alternatively, you can make twice baked potatoes with sour cream. However, during testing, I found the sour cream to be too rich. This casserole is already packed with butter and cheese, and the sour cream just took it over the edge for me. The cream cheese is enough to give it the velvety texture without taking it overboard on richness.
  • Cheddar cheese. This recipe works with mild, medium, or sharp cheddar cheese. If you have a personal preference, go with that. During testing, I landed on medium cheddar cheese to be the favorite for my personal taste. I felt it was just enough of the sharpness without the cheddar completely taking over. With both mild and medium, the flavors of butter, green onion, and the garlic salt were more prevalent than with sharp cheddar cheese, which competed with these flavors.
  • Scallions. Aka green onion.

If you are making these Twice Baked Potatoes from leftover mashed potatoes, you will just need your leftover mashed potatoes, cream cheese, cheddar cheese, and scallions.

ingredients for twice-baked mashed potatoes - garlic salt, cream cheese, cheddar, potatoes, green onions, milk, pepper, butter

How to Make Mashed Potatoes from Scratch

Start by Prepping Your Potatoes

Start by peeling your potatoes. If you like some skins in your mashed potatoes, you can leave some pieces of the peel on, but I really like to peel them until they are completely clean.

You can compost the potato skins or make these Crispy Potato Skin Chips.

Once peeled, roughly chop the potatoes into wedges, just to speed up their cooking time. They in no way have to be uniform but try to make them roughly the same size so they will boil evenly.

I usually just cut my russet potatoes into 4 or 5 pieces.

Six peeled russet potatoes on a chopping board.
Peel the potatoes first. If you like some skins in your potatoes, you can leave some little pieces on.
Peeled and chopped russet potatoes on a chopping board next to a sharp knife.
Roughly chop the potatoes into smaller wedges to speed up their cooking time.

Boil the Potatoes until Fork-Tender

Bring about 10 cups of water to a boil. Once your potatoes are prepped, carefully add them to the boiling water.

Boil the potato wedges for about 15-20 minutes, until you can easily pierce them with a fork.

Then, strain and add the potatoes to a large mixing bowl.

Using a fork to test if boiled potatoes are cooked.
Boil your prepped potatoes for 15-20 minutes until they are fork-tender.

Smash and Whip Your Potatoes

For the smoothest, creamiest, lump-free mashed potatoes, use a potato masher. Use it to completely mash your boiled potatoes until there are no visible lumps.

Then, add the butter, cream cheese, milk, garlic salt, and pepper. Use a hand mixer to whip. The heat from the potatoes will soften the butter and cream cheese, making everything easy to combine.

You really want to whip the potatoes until they’re super creamy and take on a little volume as you whip air into them.

Using a potato masher to smash boiled potatoes.
Use a potato masher to smash the potatoes and remove any lumps.
Adding milk to smashed potatoes to whip.
Add the butter, cream cheese, milk, garlic salt, and pepper, and use a hand mixer to whip until smooth and creamy.

How to Make Twice-Baked Mashed Potatoes (From Fresh Mashed Potatoes or from Leftovers)

Why You Should Use Up Leftovers Mashed Potatoes

It is estimated that 40% of food gets tossed annually in the United States. Of that 40%, half of that food waste happens in our homes. This means that reducing our individual contributions to food waste can really make an impact!

For a full debrief on this subject, check out my article on Food Waste.

Green tip: It is estimated that a whopping 40% of food gets tossed annually in the United States. Being cognizant of your contribution to waste can make an impact!

The Key to Making Twice-Baked Potatoes with Leftover Mashed Potatoes

If you are making this as a leftover mashed potatoes recipe, there is one key to getting this recipe right.

Add the cream cheese to the leftover mashed potatoes and use a hand mixer to whip them together. We’re looking for super creamy and airy mashed potatoes to start the casserole with.

You can do this with the leftover mashed potatoes cold, but make sure your cream cheese is softened so it can easily whip into the mashed potatoes.

Large mixing bowl with leftover mashed potatoes whipped with cream cheese.
If you are making this Mashed Potato Casserole with leftover mashed potatoes, make sure to whip the leftovers with the cream cheese.

Prep Your Cheese and Onions

Whether you are making this recipe from scratch or using this casserole and a recipe for leftover mashed potatoes, the steps from here on out will be the same.

If you are making it from scratch, you can prep your cheese and onions while your potatoes are boiling.

For the scallions aka green onions, it’s as simple as cleaning them, chopping off those little hairy white ends, and dicing them. Line them up on your chopping board and dice them simultaneously for a quick and easy way to dice them.

As for the cheese, you can definitely buy shredded cheese for the quickest and easiest way to whip up these twice baked potatoes. However, if you have the time and energy, I highly recommend buying a block of cheddar and grating it yourself.

Pre-shredded cheese contains extra chemical preservatives to keep the strands from sticking together that can affect both the taste and texture of the cheese.

For the quickest shredding at home, you can use a food processor with a grating attachment!

Clean scallions and chop off the "hairy ends" before dicing them.
Clean and dice the scallions and set a handful aside to garnish at the end.
Shredded cheddar cheese in a bowl next to a cheese grater.
Grate the cheddar cheese and divide it in two. Save half to add on top before baking.

Add the Scallions and Cheese into the Mashed Potatoes

Set aside half of the cheddar cheese and a handful of scallions to use later.

Add the rest of the scallions and one half of the cheese to your mashed potatoes. Use a rubber spatula to fold the scallions and shredded cheese into the mashed potatoes.

Adding scallions to cheesy mashed potatoes.
Add the cheddar cheese and scallions to the whipped cream cheese mashed potatoes.

How to Bake Mashed Potatoes into a Casserole

Add your cheesy mashed potato mixture to a 9 x 13 casserole dish. Add the rest of the cheese on top.

Then, bake the mashed potatoes on the top rack of your oven at 350°F for 30-35 minutes. Then, bring your oven up to broil (500°F) until the cheese starts to bubble and brown.

Make sure to watch it closely when your oven is on broil. It can go from bubbly to burnt really fast—sometimes all it needs is a quick 30 seconds!

Mashed Potatoes with cheddar cheese and scallions in a casserole dish.
Add your cheesy potatoes to a 9×13 casserole dish.
Mashed potatoes in a casserole dish topped with a layer of shredded cheddar cheese.
Bake on the top rack for 30-35 minutes and then finish off on broil until the cheese starts to bubble and brown.

Serving Your Twice-Baked Mashed Potatoes

These Twice Baked Mashed Potatoes are versatile and make a delicious, creamy, cheesy companion to any many dish. It’s also an outrageously delicious side for Thanksgiving dinner.

Here are some of my favorite mains to serve this cheesy potato casserole up with:

  • Portobello Mushroom Steak. A hearty and savory vegetarian dish featuring thick Portobello mushrooms marinated and grilled to steak-like perfection.
  • Pistachio Crusted Salmon. Succulent salmon fillets coated in a crunchy pistachio crust, creating a delightful blend of textures and flavors.
  • Blackened Cod. Flaky cod fillets seasoned with a bold blend of spices and seared to perfection, delivering a spicy and smoky seafood experience.
Twice Baked Mashed Potatoes on a plate with a fork.

How to Properly Store and Reheat Leftover Mashed Potato Casserole

These Twice-Baked Mashed Potatoes will stay fresh for about 5 days in the refrigerator in an airtight container. You can also freeze them for up to a full year!

To reheat, preheat your oven to 350°F and transfer the leftovers to an oven-safe dish. Cover with aluminum foil and cook for about 15-20 minutes until heated through.

If your mashed potato casserole is frozen, you can allow it to thaw overnight before following the reheating guidelines above, or just add about 10 minutes to your reheating time.

Green tip: Properly storing, reheating, and enjoying your leftovers will help to minimize your contribution to food waste!

Twice-Baked Mashed Potato Side Dish Frequently Asked Questions

What’s the difference between mashed potatoes and twice baked potatoes?

Mashed potatoes are boiled, then smashed. After smashing the boiled potatoes, you can add fillings and toppings. On the other hand, twice baked potatoes are baked until tender before adding the fillings/toppings and then baking again.

Additionally, you can make twice baked mashed potatoes, which are boiled and mashed and then baked with cheese to make a crispy cheesy topping.

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Why You Should Make these Creamy Twice-Baked Mashed Potatoes

  • The textures! Between the creamy, velvety mashed potatoes and cheesy crispy top layer, this potato casserole is the ultimate in mouthfeel.
  • The flavors. Everything you love about mashed potatoes plus cheese and green onions. Enough said.
  • They’re resourceful! This cheesy potato casserole can be made fresh or from leftover mashed potatoes!

If you’re loving these Twice-Baked Mashed Potatoes and want more delicious potato recipes, check out this Mushroom Stew with Potatoes and Pan-Fried Potatoes and Onions.

Twice Baked Mashed Potato Casserole with Scallions

Creamy Twice-Baked Mashed Potatoes (Great for Leftovers!)

5 from 5 votes
Marley Goldin
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These Twice Baked Mashed Potatoes takes creamy mashed potatoes and bakes them with cheese and green onions for the ultimate potato side dish.
Prep Time 25 minutes
Cook Time 30 minutes
Total Time 55 minutes
Servings 8 servings


Homemade Mashed Potatoes

  • 2 ½ pounds potatoes (russet or Yukon gold )
  • ¼ cup unsalted butter (softened)
  • cup milk of choice
  • 1 teaspoon garlic salt (*see notes)
  • ¼ teaspoon black pepper

Twice Baked Mashed Potatoes

  • 4 cups mashed potatoes (leftovers, or use recipe above)
  • 4 ounces cream cheese at room temperature (light or regular)
  • 2 ounces green onion (aka scallions)
  • 8 ounces cheddar cheese (mild, medium or sharp-I use medium)
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Homemade Mashed Potatoes

  • In a large pot, bring 10 cups of water to a rolling bowl.
  • Peel your potatoes and chop them into wedges to speed up the cooking time. If you like skins in your mashed potatoes, you can leave some pieces on when you peel them.
    Peeled potatoes cut into wedges.
  • Carefully add the prepped potatoes to the boiling water and boil for 15-20 minutes until the potatoes are fork-tender.
    Poking boiled potato with a fork to check if it's tender.
  • Once your potatoes are ready, strain and add the potato chunks to a large mixing bowl and use a potato masher or large fork to mash the cooked potato.
    Smashed Boiled Potatoes for Twice Baked Mashed Potatoes
  • Add the butter, milk, garlic salt, and black pepper and whip with a hand mixer on high until smooth and airy.
    Super smooth whipped mashed potatoes

Twice Baked Mashed Potatoes

  • Preheat your oven to 350°F and grate your cheese (if using a block) and dice your scallions.
  • To a large mixing bowl, add the cream cheese and mashed potatoes and use your hand mixer on high to combine. (If you are using leftover mashed potatoes, it's okay if they are cold).
    Whipped Mashed Potatoes with Cream Cheese
  • Set aside half of the cheese and a handful of scallions. Use a rubber spatula to fold the rest of the cheese and scallions into the cream cheese mashed potatoes.
    Large bowl of creamy mashed potatoes with shredded cheese and green onions.
  • Transfer the potatoes into a 9 x 13 casserole dish and use your spatula to smooth out the top.
    Creamy mashed potatoes with cheese and green onions in a casserole dish.
  • Add the remaining cheese in a thin layer on top of the potatoes.
    Mashed potatoes in a casserole dish topped with a thin layer of shredded cheddar cheese.
  • Bake on the top rack for 30-35 minutes. If after 30 minutes the cheese on top is not bubbling and starting to brown, turn your oven up to broil (500°F). Watch it closely and remove from the oven immediately once the cheese starts to bubble and brown (sometimes this happens in as quick as 30 seconds!). Garnish with remaining scallions and enjoy.
    Twice Baked Mashed Potato Casserole with Scallions

Pro Tips

  • You can make this recipe with less than 4 cups of leftover mashed potatoes! For every cup of leftover mashed potatoes, use 1 ounce cream cheese, ½ ounce scallions, and 2 ounces cheddar cheese, and adjust the casserole dish size as needed.
  • *If you don’t have garlic salt on hand, you can use ½ teaspoon garlic powder and ½ teaspoon salt in place of 1 teaspoon garlic salt in this recipe. 
  • Want more spuds? Check out this list of best potato recipes!

Share This Recipe

Course Sides
Cuisine American
Diet Vegetarian
Keyword Mashed Potatoes, Potato, Potato Casserole, Thanksgiving Leftovers, Twice Baked Mashed Potatoes, Twice Baked Potatoes
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