Starting on the outer edge of the cookie and working your way to the center, ice each cookie with the white cookie icing. Make sure it's a fairly thick layer. Let the white icing harden and set.
Take the gel icing and carefully make strands from one side of the cookie to the other. You can make your lines straight or curled or both.
Before your gel icing sets, place one of each color M&M on your black icing. For a cleaner look, make sure the "m" is facing down.
Let your cookie set at room temperature, or you can place them in the freezer just for a brief time.