1Heat oven to 350°F (325°F for dark or nonstick pans). Grease 2 (9-inch) round cake pans with shortening or cooking spray.
2Make cake mix as directed on box, using water, oil and eggs and adding 1/2 cup lemonade drink mix. Pour batter into pans. Bake as directed on box for 9-inch rounds. Cool 10 minutes; remove cakes from pans to cooling racks. Cool completely.
3In large bowl, beat all frosting ingredients with electric mixer on low speed until blended, then on medium speed 2 to 3 minutes until fluffy. (If frosting is too thick, add 1 to 2 teaspoons more cream.)
4Place 1 cake layer on serving plate; spread with frosting. Top with second cake layer. Frost top and side of cake with remaining frosting. Garnish with lemon peel and mint.