Unwrap pan. Place a rectangular platter on top of pan, and flip over to invert cake onto platter. Remove pan, and carefully peel off plastic wrap. Spread reserved refrigerated 1 cup whipped-cream mixture over top and sides of cake. To decorate, grate zest from whole lemon over top, or garnish with candied lemon peel, if using. Cake may be lightly wrapped in plastic wrap and stored in refrigerator for up to 3 days.