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-by-9-by-2-inch baking pan. Bake at 350 degrees 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.