3 1/2 tbsp. cornstarch
1 c. sugar
1 tbsp. lemon rind, grated
1/2 c. fresh lemon juice
3 egg yolks, slightly beaten
1 c. milk
1/4 c. butter
1 c. cultured sour cream
1 graham cracker pie crust
Cool Whip

Combine sugar, cornstarch, lemon rind, juice, egg yolks and milk in heavy saucepan; cook over medium heat until thick. Stir in butter and cool mixture to room temperature. Stir in sour cream and pour filling into pie shell. Cover with Cool Whip. Store in refrigerator.