1. Heat oven to 350 degrees F. Line a 15-1/2x10-1/2-inch jelly-roll pan with foil; lightly coat foil with vegetable cooking spray.
2. Make batter for one recipe White Cake. Spread batter evenly in prepared pan. Bake 20 minutes, until toothpick inserted in center comes out clean.
3. Cool cake in pan on large wire rack 10 minutes; invert cake onto rack. Remove pan and foil; cool completely. Repeat process with another recipe White Cake.Make Buttercream::
4. Beat the 6 tablespoons butter in large bowl with electric mixer until smooth. Add the 2 cups confectioners sugar, the 3 tablespoons heavy cream and the 1/2 teaspoon vanilla; beat until light and fluffy. Makes 1-1/3 cups.
5. Stir chopped strawberries into Buttercream. Place 1 cake layer on large platter; tuck four strips of wax paper under cake. Brush top of cake with melted jelly. Spread Buttercream over jelly; top with second cake layer.
6. Beat the 2 cups cream and the 1/4 cup confectioners sugar in large bowl on medium-high speed of electric mixer until stiff peaks form. Spread over top and sides of cake. Remove wax-paper strips. Garnish cake with sliced strawberries, blueberries and mint sprigs, if desired. Refrigerate up to 2 hours before serving. Makes 24 servings.
1. Combine all-purpose flour, baking powder and salt in bowl. Beat softened butter in large bowl on medium-high speed of electric mixer until smooth. Gradually beat in sugar, scraping side of bowl occasionally with rubber spatula, until light and fluffy, about 5 minutes. Add egg whites; beat 1 minute more. Beat in vanilla extract. With mixer at low speed, add dry ingredients alternately with milk, beginning and ending with dry ingredients, until blended.