Heat oven to 350°F (325°F for dark or nonstick pans). Make, bake and cool cake as directed on box for two 8-inch or 9-inch round pans.
In chilled medium bowl, beat whipping cream and powdered sugar with electric mixer on high speed until stiff peaks form. Fold in lemon curd and lemon peel.
Place 1 cake layer, rounded side down, on serving plate. Spread with 1 cup of the lemon mixture to within 1/4 inch of edge. Top with second layer. Frost side and top of cake with remaining lemon mixture. Store loosely covered in refrigerator.