Place one of the cakes on cardboard cake round
and top with mint buttercream frosting. Spread out the frosting with an offset spatula. Put some frosting in a decorating bag and pipe a wide rim of frosting around the outside of the cake to hold the ganache in place. Pour about 1/3 cup of chocolate mint ganache in the center of the cake and spread it out with an offset spatula. Repeat with the second cake layer.