Make your sugar cookies. You want them to be irregular in shape so that they look like blobs of melting snow once they are iced. We used an oval cookie cutter and then reshaped them to make them a bit irregular.
Frost your cookies with royal icing and let some of the icing drip off the sides to resemble melting snow.
Soften one marshmallow per cookie in the microwave for about 30 seconds. Transfer to the cookie and shape as you like to resemble melting snow.
Decorate as you wish. There are lots of versions out there, but we just got out all of our holiday sprinkles and my creators went to work.
Source: The Decorated Cookie