For the Cookies
Preheat your oven to 350 and line a baking sheet with parchment.
In a large mixing bowl, mix together the cake mix, melted butter, and eggs. You should end up with a sticky dough. If the dough is too dry and not sticky, add 1 tbsp. water, and mix well again.
Use a 1 1/2 inch cookie scoop to scoop the cookies into your parchment lined baking sheet, about 2 inches apart.
Bake for 9-11 minutes. Allow the cookies to cool for 4-5 minutes on the baking sheet, then move to a wire rack to cool completely.
For the Chocolate Ganache
In a medium saucepan, add the semi sweet chocolate and heavy cream.
Heat over medium low heat, stirring constantly, until chocolate is melted. Remove from the heat and set aside.
For the Mint Frosting
Beat together the butter and powdered sugar. You'll get a super light and fluffy mixture.
Add the mint extract and 1-2 tsp. of the green gel color, and mix well to combine. Frosting will be thick.
Use the milk, about 1-2 tbsp. at a time to thin out the frosting. You want it to still be stiff enough to hold its shape.
Once the ganache has cooled, add the frosting to your cookies, spreading it so that there is a small dip or divot in the frosting towards the center of each cookie. This is to hold the ganache.
Use a small spoon to carefully spoon a bit of the ganache onto each cookie.
Set the cookies in the refrigerator for about 5 minutes to set.
Chop the mint candies roughly, and then add to the cookies.