Use serrated knife to cut one-fourth off each cake to form a straight edge about 6 1/2 inches long as shown in diagram (discard small pieces of cake or use for making small purse shown in video). Spread slightly less than 1/4 cup frosting on bottom side of 1 layer; spread about 1 tablespoon frosting on cut side. Stand cake layer, cut side down, on serving plate. Spread about 1 tablespoon frosting on cut side of second layer; place bottom side of layer on frosting of standing layer, matching cut edges. Lightly press layers together to form purse cake.