Preheat oven to 350 degrees.
Line 9x9 baking pan with parchment paper.
Line the bottom with graham cracker squares. You may have to half the squares to fit the ends.
In a medium bowl, combine chopped chocolate, cocoa powder and espresso. Set aside.
In another medium bowl, combine granulated sugar, brown sugar. Set aside.
Crack eggs in a small bowl. Set aside.
Place cubed butter in a medium saucepan over medium heat. Frequently stir. The butter will lightly boil and start to foam. When it turns a light golden brown and smell nutty, pull from the heat.
Immediately pour the brown butter into the chocolate mixture and whisk together until chocolate is melted. Set aside to cool down 10-15 minutes.
Add the eggs to the sugars and mix for 2 minutes. I used an electrical hand mixer.
Add the sugar mixture to the chocolate mixture in a steady stream. While pouring, whisk at the same time until just combined.
Fold the flour into the wet mixture and combine until the flour is well incorporated.
Pour the chocolate batter over the graham cracker layer. Smooth batter out.
Bake for 28- 30 minutes.
Once you remove the brownies from the oven, add the marshmallow layer.
Put the broiler on low and place the brownies back in the oven. Broil 2-3 minutes. Keep an eye on the marshmallows, they can brown fast.
Cool in the pan for 30 minutes. Remove the brownies with the parchment paper and cool on wire rack for at least 30 minutes before cutting into it.
