Preheat oven to 350F and line an 8x8 pan with parchment, leaving an overhang.

Mix graham cracker crumbs with melted butter until it looks like wet sand.

Press firmly into the bottom of the pan in an even layer.

Bake 8 minutes, until the edges look lightly golden.

Remove from oven and immediately scatter chopped chocolate over the hot crust; let sit 2 minutes until glossy, then spread into an even layer.

Scatter mini marshmallows evenly over the chocolate.

Switch oven to broil and broil 1 to 2 minutes, watching constantly, until marshmallows are toasted golden brown in spots.

Cool completely in the pan, at least 20 minutes, before lifting out with the parchment.

Cut into bars once fully cooled and firm (warm bars will pull apart instead of slicing clean).