For the crust, beat the butter in a medium mixing bowl with an electric mixer on medium to high speed for 30 seconds. Add the 1/4 cup granulated sugar. Beat until thoroughly combined. Beat in the 1 cup flour and about half of the nuts until mixture is crumbly.
Press mixture into the bottom of an ungreased 8x8x2-inch baking pan. Bake in a 350 degree F oven for 10 minutes or until lightly browned.
Meanwhile, in a mixing bowl stir together the eggs, the 3/4 cup granulated sugar, the 2 tablespoons flour, orange peel, lemon peel, orange juice, lemon juice, and baking powder. Beat for 2 minutes at medium speed or until combined. Pour over hot baked layer. Sprinkle with remaining nuts.
Bake about 20 minutes more or until light brown around the edges and the center is set. Cool on a rack. If desired, sift powdered sugar over top. Cut into bars. Store bars, covered, in the refrigerator. Makes 20 bars.