Box of store brought brownie mix, made up to instructions
4 cups large marshmallows (or enough to cover 8×8 square pan)
For the crust: Lightly butter the foil with some of the melted butter. Stir the rest of the butter together with the crumbs, sugar, and salt in a medium bowl. Press the crumb mixture evenly over the bottom of the pan. Bake until golden brown, about 20 minutes.
Meanwhile, make the brownie mix. Pour brownie batter into the prepared pan. Bake until done according to instructions or until toothpick comes out clean.
Remove from the oven and carefully position a rack about 6 inches from the broiler and preheat on low. Layer marshmallows across the top and toast under the broiler until golden, keep an eye on it, it can go quick! Cool on a rack, gently removing the brownies from the pan using the aluminum flaps. Carefully separate any marshmallow from the foil and fold away. Cut and ENJOY!