Prepare chocolate sugar cookies according to recipe directions. Allow to cool and then turn each cookie over. Top each cookie with a half of a marshmallow. Place the baking sheet of cookies under a broiler until the marshmallow becomes slightly melty and lightly browned. Remove from the oven and allow to cool for a few seconds. Top the marshmallow with a second chocolate sugar cookie and lightly press down on the top cookie to form the sandwich cookies. Repeat until all of the chocolate marshmallow sandwich cookies have been made.
Allow to cool for a few minutes before transferring to a platter for serving.