Use a knife to slice cake layers in half horizontally. Use a pastry brush to brush each layer with lemonade concentrate; set aside.
Stir 1 teaspoon of lemon extract into each can of frosting; set aside.
To assemble cake: frost and stack the cake layers on top of each other.
Decorate cake with clusters of mint sprigs, blueberries, and quartered lemon slices.
Recipe courtesy of Sandra Lee