Bake cookies according to manufacturer's suggestions except roll them just a little thicker. You may need to cook them a slight bit longer (don't overcook). Cool completely.
Mix powdered sugar with milk to make a thick paste. Too thick, add just a little milk. Too thin, add more powdered sugar. Spread sugar paste over cookies generously enough to adhere candies. Place m&m's type candies (all m's facing down or all facing up for a uniform appearance) in a pleasing pattern over surface of cookie. Let dry completely. Store in airtight container in cool place.