*One large lemon may be used for both the grated lemon rind and the ¼ cup lemon juice.

Combine sugar, cornstarch, lemon rind, butter, lemon juice, milk and egg yolks in a heavy saucepan. Cook over medium heat until smooth and thickened, stirring constantly. Remove from heat and fold in sour cream. Pour into graham cracker crust and chill, uncovered for 2 hours. Top with cool whip. Yield: One 9-inch pie.