1. Prep the Oven and Pan

Preheat the oven to 350°F (175°C). Line a 9×9-inch pan with parchment paper, ensuring all sides are covered for easy removal.

2. Create the Graham Cracker Layer

Place a single layer of graham crackers at the bottom of your prepared pan. You may need to cut some graham crackers into smaller pieces to cover the base completely. Set this aside.

3. Prepare the Chocolate Mixture

In a medium bowl, combine the chopped chocolate, cocoa powder, and espresso powder. Set it aside.

4. Brown the Butter

In a medium saucepan, melt the butter over medium heat. Stir occasionally as the butter melts. Once it begins to bubble and foam, continue stirring until the milk solids brown and the butter smells nutty. Immediately remove it from the heat and pour over the chocolate mixture to melt. Stir until smooth, then set it aside to cool for 10-15 minutes.

5. Mix the Brownie Batter

In a large mixing bowl, whisk together the eggs, granulated sugar, and brown sugar for 2 minutes until smooth. Slowly stream in the cooled chocolate mixture while whisking. Once combined, gently fold in the flour until just mixed.

6. Bake the Brownies

Pour the brownie batter over the graham cracker layer in the pan, spreading it evenly into the corners. Bake for 28-30 minutes or until the edges are set, and a toothpick inserted in the center comes out mostly clean but with a few moist crumbs.

7. Broil the Marshmallows

After baking, move the oven rack to the top position and arrange the marshmallows over the brownies. Turn on the broiler and toast the marshmallows for 2-3 minutes until golden and bubbly. Be sure to watch closely, as marshmallows can burn quickly under the broiler.

8. Cool and Slice

Allow the brownies to cool in the pan on a wire rack for at least 30 minutes. Afterward, lift the brownies out of the pan using the parchment paper overhang. Let them cool completely before slicing. To avoid sticking, rub a little cooking oil on your knife before cutting through the marshmallow topping.