1. Heat oven to 350°F. Grease and flour 8-inch square baking pan.
2. Stir together flour, granulated sugar, brown sugar, cocoa, baking soda and salt in medium bowl. Add water, oil, vinegar and vanilla; beat with whisk or spoon until smooth. Pour batter into prepared pan.
3. Bake 18 to 20 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pan to wire rack. Cool completely. Transfer to cutting board. Using 3-1/4 inch heart-shaped cookie cutter, cut cake into 4 hearts. Spread CHOCOLATE FROSTING on top of two hearts; place remaining two hearts on top. 2 small cakes.
1 tablespoon butter or margarine
2/3 cup powdered sugar
1 tablespoon HERSHEY'S Cocoa
2 to 3 teaspoons milk
1/8 teaspoon vanilla extract
Place butter in small microwave-safe bowl. Microwave at MEDIUM (50%) 20 seconds or until butter is melted. Stir together powdered sugar and cocoa; add to butter mixture alternately with milk, beating with spoon or whisk until smooth. Stir in vanilla. About 1/3 cup frosting.