About 2-1/4 hours before serving or early in day: Preheat oven to 375°F. From 1 lemon, with vegetable peeler, cut peel into 1-inch-wide strips; wrap in plastic wrap; reserve for garnish. From remaining 2 lemons, grate peel. Squeeze juice from all 3 lemons. In large bowl, with mixer at low speed, beat egg-white ingredient packet from cake mix with orange juice and 1 cup water until blended. With mixer at high speed, continue beating 5 to 10 minutes, scraping bowl occasionally with rubber spatula, until stiff peaks form. With rubber spatula, fold in cake-four ingredient packet, lemon extract, and grated lemon peel just until four disappears. Pour batter into ungreased 10-inch tube pan with removable bottom. Bake 30 to 35 minutes until cake springs back when lightly touched. Invert cake in pan on funnel or bottle; cool in pan. While cake is cooling, prepare lemon peel for garnish: With knife, trim white membrane, if any, from reserved lemon-peel strips; cut into matchstick-thin strips. With metal spatula, carefully loosen cake from pan; place cake, bottom-side up, on cake plate. In 1 -quart saucepan over high heat, heat sugar and 1/2 cup lemon juice to boiling. Reduce heat to medium; cook, stirring occasionally, until mixture is reduced to 1/2 cup, about 5 minutes. With long wooden skewer, poke many holes in cake; with pastry brush, brush lemon-juice mixture over top and side of cake. In medium bowl, with spoon, mix confectioners sugar and 2 tablespoons plus 2-1/2 teaspoons lemon juice until smooth, to form a thick but spreadable frosting (stir in more lemon juice, 1/4 teaspoon at a time, if frosting is too stiff). Reserve any remaining lemon juice for use another day. With small metal spatula, spread frosting over top of cake, allowing it to drip down side of cake. Garnish cake with lemon-peel strips and mint sprigs. Makes 16 servings. Each serving: About 160 calories, 0 g fat, 0 mg cholesterol, 200 mg sodium. pc 147