Shortbread Lemon Bars

1 1/2 cups all-purpose flour
1/2 cup confectioners' sugar
1 tsp grated lemon peel
3/4 cup cold butter or margarine

FILLING:
4 eggs
2 cups sugar
1/3 cup lemon juice
1/4 cup all-purpose flour
2 tsp grated lemon peel
2 tsp grated ornage peel
1 tsp baking powder

TOPPING:
2 cups (16 oz) sour cream
1/3 cup sugar
1/2 tsp vanilla extract

In a food processor, combine flour, confectioners' sugar, and lemon and orange peel. Cut in butter until crumbly; process until mixture forms a ball. Pat into a greased 13 x 9 x 2-inch baking pan. Bake at 350*F for 12-14 minutes or until set and the edges are lightly browned.
Meanwhile, in a mixing bowl, combine the filling ingredients; mix well. Pour over hot crust. Bake for 14-16 minutes or until set and lightly browned.
Meanwhile, in a bowl, combine topping ingredients. Spread over filling. Bake 7-9 minutes longer or until topping is set.
Cool on a wire rack.
Refrigerate overnight.
Cut into bars just before serving.
Yield: 3 dozen