Preheat the broiler. Pour the chocolate chips into a 9-inch ovenproof skillet. Add milk, then stir the mixture on the stove-top over medium-low heat until the chips are melted, about 3 minutes. Top the chocolate with a layer of marshmallows. Place the skillet under the broiler for a minute or two, watching it carefully, until the marshmallows turn golden brown. Serve it with graham crackers and spoons for scooping (be sure to warn kids not to touch the skillet while it's hot).