1Heat oven to 350°F (325°F for dark or nonstick pans). Line two 8-inch square pans with foil, letting foil hang 2 inches over 2 opposite sides of pans. Grease or spray bottoms and sides of foil.
2Make cake batter as directed on box. Pour into pans. Bake 25 to 32 minutes or until toothpick inserted in center of cake comes out clean. Cool 15 minutes.
3In small bowl, mix powdered sugar and lemon juice. Poke top of warm cake every 1/2 inch with long-tined fork, wiping fork occasionally to reduce sticking. Drizzle and spread lemon mixture over top of cake. Refrigerate about 2 hours or until chilled. Remove cakes from pans by lifting with foil; peel away foil.
4In small microwavable bowl, microwave frosting uncovered on High 15 seconds. On serving plate, place 1 cake, rounded side down; trim if necessary so layer rests flat. Spread with half of frosting. Top with second cake, rounded side up. Frost top of cake with remaining frosting. Garnish with lemon drop candies. Store loosely covered.