Over medium heat, add milk, cream, and sugar to a large saucepan. Heat and stir until the sugar is dissolved.
¼ cup milk, ½ cup heavy cream, ½ cup granulated sugar
Add your cornstarch and whisk until there are no visible lumps. Continue to heat, stirring frequently, until your sauce thickens (cornstarch will start to thicken sauce once it reaches 295°F).
1 tablespoon cornstarch
Add your vanilla extract and stir to combine. Assess the consistency. To thicken, continue to heat. If you are happy with the thickness, remove it from heat.