Preheat oven to 350°.

Mix together the cake mix, egg and butter. The less mixing the better, and since the butter is melted, you can just use a large spoon to easily mix the cookie dough. I think that the mint flavor from the M&Ms is enough, but you if you want a little bit more mint flavor, add 1/2-1 tsp of mint extract to the cookie dough and mix in completely. Fold in the M&Ms.

Use a cookie scoop to scoop out 1 Tablespoon sized balls. Place the cookie dough balls on a baking sheet and bake for 8-9 minutes. Let the cookies cool on the baking sheets for a few minutes before transferring to wire racks to cool completely.

Cookies can be stored in an airtight container for 3-4 days, or in the freezer for up to a month.