Mix together cake mix, eggs and shortening until well combined. The dough will be pretty thick.
Roll dough into 1-inch balls, making sure they are all similar in size.
Place dough onto ungreased cookie sheet and bake for 8 minutes.
Immediately transfer cookies to a cooking rack.
To make the frosting, mix together butter, milk, powdered sugar, peppermint extract and as much green food coloring as desired (I used 8 drops) until smooth.
Spread onto cooled cookies and sandwich together.
Notes
These chocolate and mint cookies are divine as they are, but if you want to take them one step further you can always add some yummy chocolate ganache! Drizzle it, dip it, or even smother it in the chocolate ganache oh cannot go wrong.