How to Make It
Preheat oven to 350°.
Place sugar and butter in a large bowl; beat with a mixer at medium speed until well blended (about 5 minutes). Add eggs, 1 at a time, beating well after each addition. Add rind and juice; beat well. Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Combine flour and next 4 ingredients (through salt), stirring well with a whisk. Add flour mixture and buttermilk alternately to butter mixture, beginning and ending with flour mixture; mix after each addition.
Spoon batter into a 9-inch square metal baking pan coated with cooking spray. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool cake in pan 10 minutes on a wire rack; remove from pan. Cool completely on wire rack.
Cut shortcake into 9 squares. Reserve 4 squares for Brandied Peach Shortcakes and 3 squares for Mixed Berry Trifles; freeze remaining 2 squares for another use.