Melt butter and add to graham cracker crumbs, mixing until well
combined to make crust.
Prepare muffin/cupcake pan by placing evenly divided butter and
crumb mixture into the bottom of each of the 12 cups, saving
about 1/4 cup to use as topping later. I used a spoon to make sure
crumb mixture was firmly packed into the bottom.
Place milk chocolate chips and whipping cream into a small bowl
and microwave in 30 second increments, stirring in between, until
melted and smooth.
Spoon chocolate into a zip top bag, cut a tip off and evenly pipe
chocolate into the center of each cup, on top of the crust.
Divide Marshmallows among cups.