1. In a saucepan combine the 1 cup sugar and cornstarch. Add milk, egg yolks, butter or margarine, and lemon peel. Cook and stir over medium heat till thickened and bubbly; cook and stir 2 minutes more. Remove from heat; stir in lemon juice. Transfer to a bowl; cover surface with plastic wrap and chill. When cool, stir the sour cream into mixture, then fold in blueberries; pour mixture into pastry shell. Cover and chill at least 4 hours. If desired, garnish with whipped cream lemon slices.