- 4 tablespoons unsalted butter, melted
- 1 cup graham cracker crumbs

- 10 tablespoons (1¼ sticks) unsalted butter
- 1¼ cups (8¾ oz) granulated sugar
- 3/4 cups plus 2 tablespoons (2½ oz) unsweetened cocoa powder
- 1/4 teaspoon salt
- 1 teaspoon vanilla extract
- 2 large eggs
- 1/2 cup (2¼ oz) all-purpose flour
- 1 cup milk chocolate chips
- 1/2 cup marshmallow fluff
-1 cup mini marshmallows

1. Preheat the oven to 325°F. Line an 8-by-8-inch baking pan with aluminum foil or parchment paper, leaving an overhang on the sides. Spray with nonstick cooking spray; set pan aside.
2. In a bowl, combine melted butter and graham cracker crumbs. Press into the prepared pan. Set aside.
3. In a large microwave-safe bowl, combine butter, sugar, cocoa, salt, and heat on high power to melt, about 45 seconds. Stop to stir, and heat in 10-second bursts until mixture has melted and can be stirred smooth (mine took 45 seconds + 15 seconds). Batter will be very granular.
4. Add the vanilla, eggs, and stir vigorously until the batter is thick, shiny, and well blended. Add the flour and stir until you cannot see it any longer. Fold in the chocolate chips. Pour half the batter into the prepared pan and spread evenly.
5. Dollop half of the marshmallow fluff all over the batter and swirl slightly with a knife. Spread the remaining batter carefully over the marshmallow fluff. Repeat with the remaining marshmallow on top of the brownie batter. With a knife, carefully swirl the marshmallow fluff slightly into the batter. Don’t swirl too much!
6. Bake until a toothpick in the center emerges slightly moist with batter, about 25 minutes. Increase oven temperature to 375°F. Top with mini marshmallows and bake for another 3-5 minutes or until marshmallows are lightly browned on top.
7. Cool brownies completely before cutting into 16 equal squares with a very sharp knife.
8. Brownies will keep in an airtight container at room temperature or in the refrigerator for up to 1 week, or in the freezer for up to 3 months.