Place an oven rack in the top position and preheat the oven to 450 degrees F. While the oven heats, put a 10-inch cast-iron or stainless-steel skillet in to heat.
Carefully remove the hot skillet and sprinkle the chocolate and butterscotch chips in the bottom. Drizzle the cream over the top and then top with the marshmallows in an even layer. Set the skillet on the top oven rack and bake until the marshmallows are molten and golden on top, 5 to 6 minutes.
Serve (carefully, the pan will be very hot) with graham crackers for dipping.