Put the remaining butter, powdered sugar, milk, mint extract, and food coloring in a mixing bowl and mix with an electric mixer until it forms a creamy icing. Add more powdered sugar to thicken or milk to thin as necessary. I had to use a little extra milk when i made mine.
10 
Set out the cookies to add the topping to them. I ended up flipping them over so i could work with the flat underside. Add and evenly spread the icing to the cookies. I used a tiny little spoon to dollop and spread the icing.
11 Once youre done icing all the cookies set back in the freezer to firm the icing up.
12 Just before taking the cookies back out pour the chocolate chips and coconut oil into a bowl and heat in the microwave for 20 - 30 second increments stirring between each time until chocolate is fully melted.
13 Drizzle or dollop and spread the chocolate evenly over the icing.
14 Place back in the freezer to set up the chocolate.
Note
Since there's milk in the icing make sure you store in the fridge or freezer long term.
These cookies were really good and perfect for experimentation. You can easily switch up the flavoring of the icing. My mom thought the cookies would be a good base for cookie sandwiches.