Beat butter with an electric mixer in a medium mixing bowl on medium to high speed for 30 seconds.
Add the 1/4 cup granulated sugar to the butter and beat until butter and sugar are thoroughly combined, then beat in the 1 cup flour and about 1/2 of the nuts until the mixture becomes crumbly.
Press the mixture onto the bottom of an 8 x 8 x 2 inch baking pan and bake for about 10 minutes or until lightly browned.
In a medium mixing bowl combine the eggs, 3/4 cup granulated sugar, 2 tablespoons flour, orange peel, orange juice, lemon peel, lemon juice and baking powder and beat on medium speed for about 2 minutes or until ingredients are combined.
Take the mixture and pour over hot crust, then sprinkle with the remaining nuts.
Bake the mixture and crust for about 20 minutes or until the center is set and is light brown around the edges.
Cool it in the pan on a wire rack.
Sift powdered sugar over the tip of the treat if desired and cut into bars.
Cover the bars and store them in the refrigerator.