Mix cookie mix according to directions, or prepare your favorite cut out sugar cookie recipe, then just grab a tablespoon sized ball and squish it down until it's about 1/4-1/2 inch thick. Do not worry about the shape or how lumpy it is, the more misshapen the better. Bake according to recipe directions.
Once cookies cool, spread icing around with the back of a spoon, let some dribble over the edge for a "puddle" look.
Spray a microwave safe plate with cooking spray, and place marshmallows on the plate. Set the microwave for 30 seconds, but watch the marshmallows as they cook. Stop the microwave as soon as the marshmallows start to get puffy, do not let them double in size.
Spray your fingers with cooking spray and carefully pull the marshmallows off and set them on top of the frosted cookies "puddle".
Decorate as you'd like with icing, or homemade frosting!