Bake and cool cake. Prepare batter following recipe directions. Place bakeware on cookie sheet. Bake and cool cakes following package directions.
Decorate cake. Prepare buttercream icing following recipe directions. Use 9 in. angled spatula and white icing to ice top of cake smooth.
Use 9 in. fondant roller with purple guide rings to roll out pink fondant 1/16 in. thick. Use medium cut-out from set to cut heart. Place pink heart on the center of cake. Roll out red fondant to 1/16 in. thick. Use small cut-out from set to cut heart. Brush red heart with damp brush to secure to center of pink heart.