Line a 9x13" pan with parchment paper and grease lightly.

In a bowl, stir together graham cracker crumbs and melted butter. Press evenly into the prepared pan. As is, the crust can be crumbly. If you want a firmer crust, bake for 8 minutes at 350ºF. Let cool while you prepare the fudge.

Over low-medium heat in a medium saucepan, combine butter, sweetened condensed milk, and chocolate chips. Stir frequently until the mixture is completely melted and smooth, about 3-5 minutes. Remove from heat.

Pour mixture into a prepared pan. Spread evenly. Sprinkle mini marshmallows on top and press down slightly into the fudge so they stay put. Using a kitchen torch, toast the marshmallows. Alternatively, you can put the pan under your over broiler for about 1 minute or until golden brown - watch carefully.

Refrigerate until set before cutting into 64 pieces. Store in the refrigerator for up to two weeks.