Spread the chocolate chips in an even layer in the bottom of a 9-inch cast iron skillet. They need to be in an even layer so that they melt evenly.
Bake for 3-4 minutes, or until the chocolate chips are beginning to melt.
Place the halved marshmallows in an even layer over the chocolate pieces.
Bake for 2-4 minutes, or until the marshmallows are golden brown. Keep an eye on the marshmallows starting at 2 minutes as they can quickly get overcooked.
Remove from oven and let the dip sit for about 5 minutes so the chocolate can continue to melt.
Serve with graham crackers for dipping.
Notes
Chocolate chips: Feel free to use bittersweet chocolate chips, dark chocolate chips, or milk chocolate chips depending on how sweet you would like the dip to be.
Marshmallows: Using large marshmallows helps to keep them from browning too quickly.
Graham crackers: Graham cracker dippers work well, but graham crackers can also be used.