How to Make It
Preheat oven to 350°.
To prepare cake, lightly coat 2 (8-inch) round metal cake pans with baking spray; line bottoms of pans with wax paper. Coat wax paper with baking spray.
Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt in a medium bowl, stirring well with a whisk. Combine buttermilk and low-fat milk. Combine 1 cup granulated sugar, butter, and oil in a large bowl; beat with mixer at medium speed 3 minutes or until light and fluffy. Add egg yolks, 1 at a time, beating well after each addition. Beat in 1 tablespoon rind. Add flour mixture and milk mixture alternately to butter mixture, beginning and ending with flour mixture and beating just until combined.
Place 3 egg whites and cream of tartar in a medium bowl; beat with a mixer at high speed until medium peaks form, using clean, dry beaters. Gently fold egg white mixture into batter. Divide batter evenly between prepared pans. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes on wire racks. Loosen edges with a knife, and invert cake layers onto racks. Carefully remove wax paper, and discard.
To prepare lemonade syrup, while cake layers bake, combine 1/4 cup granulated sugar and next 3 ingredients (through 1 tablespoon water) in a 1-cup glass measure. Microwave at HIGH 45 seconds or until mixture boils; stir until sugar dissolves. Cool slightly. Pierce warm cake layers liberally with a wooden pick. Brush syrup over warm cake layers until all of syrup is absorbed. Cool completely.
To prepare frosting, place chilled cream cheese, 2 teaspoons rind, and 1 teaspoon juice in a large bowl; beat with a mixer at medium speed until well combined. Gradually add powdered sugar; beat at low speed just until blended (do not overbeat). Place 1 cake layer on a plate, and spread half of frosting over top. Top with remaining cake layer. Spread remaining frosting over top of cake. Store cake, loosely covered, in refrigerator.