In a large bowl or large measuring cup, whisk together milk, cream, and egg yolks until the egg yolks are well-broken up and the mixture is thoroughly combined.

In a medium-sized saucepan, combine sugar, salt, and cornstarch and whisk together.

While still whisking, slowly drizzle egg yolk mixture into the saucepan. Go slowly so you have time to evenly incorporate the ingredients and eliminate any lumps that might otherwise form.

Turn stovetop heat to medium and whisk constantly until it begins to thicken to a pudding-like consistency. How long this takes depends on your particular saucepan and stovetop, but you can tell it’s done when the whisk leaves trails through the mixture and it coats the back of a spoon (see video for visual).

Remove from heat and pour immediately through a fine mesh strainer into a large, heatproof bowl.

Add butter, one tablespoon at a time, whisking until completely melted after each addition.

Stir in vanilla extract. Mixture should be smooth and completely combined.

Allow pastry cream to cool at room temperature for 15-20 minutes, stirring occasionally to prevent a skin from forming, then place a piece of wax paper or plastic wrap directly against the surface of the pastry cream (to prevent a skin from forming as it chills).

Transfer to refrigerator and allow to chill for several hours or up to 3 days before using.