1 1/2 c. Bisquick
3/4 c. sugar
1/3 c. cocoa
1 egg
2/3 c. milk
1/4 c. vegetable oil
1 tsp. vanilla
1/2 tsp. mint extract
Mint cream (below)

Grease and flour round cake pan, 9 inch.  Beat all ingredients except mint cream in large bowl on low speed 30 seconds.  Beat on medium speed about 4 minutes, scraping bowl constantly.  Pour into pan.  Bake about 35 minutes or until toothpick inserted is clear.  Cool 10 minutes, remove from pan and cool completely.  Carefully split cake horizontally to make two layers.  Place bottom layer of cake on serving plate and spread with 1 cup mint cream.  Top with second layer.  Frost with remaining mint cream. 

MINT CREAM
1 1/2 c. heavy whipping cream
3/4 c. powdered sugar
1/4 tsp. mint extract
3 drops green food coloring

Whip all ingredients in chilled bowl until stiff. 

Source: http://www.nancys-kitchen.com