ONE-PAN CAKE: Grease and flour 13x9x2-inch baking pan. Heat oven to 350° F. Pour batter into prepared pan. Bake 35 to 40 minutes. Cool completely. Frost. THREE LAYER CAKE: Grease and flour three 8-inch round baking pans. Heat oven to 350°F. Pour batter into prepared pans. Bake 30 to 35 minutes. Cool 10 minutes; remove from pans to wire racks. Cool completely. Frost. BUNDT CAKE: Grease and flour 12-cup fluted tube pan. Heat oven to 350°F. Pour batter into prepared pan. Bake 50 to 55 minutes. Cool 15 minutes; remove from pan to wire rack. Cool completely. Frost. CUPCAKES: Line muffin cups (2-1/2 inches in diameter) with paper bake cups. Heat oven to 350°F. Fill cups 2/3 full with batter. Bake 22 to 25 minutes. Cool completely. Frost. About 30 cupcakes. "PERFECTLY CHOCOLATE" CHOCOLATE FROSTING 1/2 cup (1 stick) butter or margarine 2/3 cup HERSHEY'S Cocoa 3 cups powdered sugar 1/3 cup milk 1 teaspoon vanilla extract Melt butter. Stir in cocoa. Alternately add powdered sugar and milk, beating to spreading consistency. Add small amount additional milk, if needed. Stir in vanilla. About 2 cups frosting.