Bring 1 1/2 cups of the milk and the granulates sugar to a boil in a saucepan. While the milk is heating, in a separate bowl, mix together the cornstarch and remaining 1/2 cup of milk. Add the egg yolks, salt and vanilla. Stir until blended. When the milk is almost boiling, add a few large spoons of hot milk to the egg yolk mixture to "temper" it. Keeping the milk at a low boil on the stove, slowly add the tempered yolk mixture to the milk stirring constantly. The mixture will begin to thicken as you are stirring. When entire yolk mixture is incorporated into the boiling milk, and the mixture is thick, remove from heat. Pour into bowl or container to cool. Dot with a little butter while still hot to prevent a skin from forming. Refrigerate until ready to use.
