1/3 c. cornstarch
1/2 c. sugar
4 c. (1 qt.) skim milk
2 tbsp. butter
1 tbsp. vanilla

Mix the cornstarch and sugar together thoroughly. Transfer to a small saucepan and add the milk. Cook, stirring constantly, over low-medium heat until the mixture is very thick. Cut the butter into 2 or 3 pieces and add them and the vanilla to the milk mixture. Stir until blended.