In a food processor, combine the flour, confectioners' sugar, and lemon and orange peel. Add butter; cover and process until mixture forms a ball.
Pat into a greased 13 x 9 baking pan. Bake for 12-14 minutes or until set and the edges are lightly browned.
In a large bowl, combine all the filling ingredients. Pour over hot crust. Bake for 14-16 minutes or until set and lightly browned.
In a small 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. Store in the refrigerator.
Recipe by Simple, Sweet & Savory at https://www.simplesweetsavory.com/luscious-lemon-shortbread-squares/