Place equal parts softened butter and flour into a bowl.

Combine the butter and flour into a smooth paste.

Pour your milk into a heavy-bottomed sauce pot. Heat the milk over a medium-high flame until it begins to simmer.

Add the sugar to the hot milk and whisk until the sugar is dissolved. Bring the milk back to a low boil.

One small piece at a time, add the butter and flour mixture to the milk.

This butter and flour mixture is also called "beurre manie". It is pronounced [burr mahn-YAY] and is French for kneaded butter. This paste is used to thicken sauces, savory and sweet.

Continue whisking the beurre manie into the milk until it has all been incorporated.

Keep whisking. You never know the thickening power of a starch until your liquid boils.

The milk will become a thick paste.

Pour the thickened milk into a clean bowl. The wider the bowl base, the better. It will help the mixture cool faster and more evenly.

Place a sheet of plastic film straight down on the top of the milk mixture.

Once the mixture has cooled to room temperature, remove the plastic film.

You will want to have the separated egg yolks ready and at room temperature.

One at a time, whisk the egg yolks into the base.

Make sure that each egg yolk is thoroughly incorporated into the base before you add another.

Continue whisking until you have a smooth, homogeneous mixture.