Melt 2 tablespoons butter or margarine; blend in 1/4 CUP sugar, 2 tablespoons cornstarch, and 34 teaspoon salt.
Gradually stir in 3/4 CUP water.
Cook, stirring constantly, till mixture thickens.
Combine 2 beaten egg yolks with 1/3 cup frozen lemonade concentrate.
Stir a small amount of hot mixture into yolk mixture; return to hot mixture and, stirring constantly, bring just to a boil.
Tint with a few drops yellow food coloring, if desired.