- Preheat oven to 350 degrees F. In a medium bowl stir together the 1 cup flour, salt, and the powdered sugar. Using a pastry blender, cut in butter until mixture resembles coarse crumbs (mixture will be dry). Press mixture into the bottom of an ungreased 8x8x2-inch baking pan. Bake for 15 to 18 minutes or just until golden.
- Meanwhile, for filling, in a large bowl beat eggs, granulated sugar, the grapefruit juice, the lemon juice, and the 3 tablespoons flour with an electric mixer on medium speed about 2 minutes or until combined, scraping sides of bowl occasionally. Stir in grapefruit peel. Pour filling over hot crust. Bake about 20 minutes more or until light brown around the edges and center is set. Transfer to a wire rack; cool. Cover; chill for 1 to 2 hours. Dust lightly with powdered sugar. Cut into bars.
From the Test Kitchen
Layer bars without powdered sugar between sheets of waxed paper in an airtight container; cover. Store in the refrigerator for up to 3 days or freeze uncut bars for up to 1 month. Dust with powdered sugar before serving.