Make cake. Level and save removed top. Make buttercream. Apply a crumb coat. Chill. Meanwhile, crumble top in a med. bowl. Blend in a heaping spoonful of buttercream. Form into a ball leaving a flat area. Coat cake with buttercream. Place ball flat side down on cake. Pour ganache over ball. Place a cone on top and press down a bit to secure. Drizzle sprinkles over ganache.