Preheat oven to 350°.Grease a 13x9 inch baking dish.In mixing bowl, combine flour, confectioners’ sugar, and citrus peel. Cut in butter (I find using forks is easiest) until mixture is crumbly. Process until mixture forms a ball. Pat crust into pan. Making it as even as possible. Bake for 12 minutes or until the edges are set and lightly brown.
Meanwhile, in a large mixing bowl, combine all filling ingredients: eggs, sugar, lemon juice, flour, lemon peel, orange peel, and baking powder; mix well. Pour over HOT crust. Bake for 14-16 minutes or until set and lightly browned.
In a bowl, combine topping ingredients: sour cream, sugar, and vanilla. Spread over filling. Bake 7-9 minutes longer or until topping is set. Cool on wire rack. Refrigerate overnight. Cut just before serving.