Preheat your oven to 350°F.
Melt the butter and chocolate chips together using a double boiler or microwave. Stir until smooth, then set aside.
In a separate bowl, whisk together the eggs, sugar, and vanilla extract until well combined.
Add the melted chocolate mixture and fold until fully incorporated.
Sift in the cocoa powder, flour, baking powder, and salt. Gently fold into the egg mixture.
Line the bottom of your baking pan with graham crackers.
Pour the brownie batter over the graham cracker layer and smooth it out.
Bake for 25 minutes or until the center is set.
Remove from the oven and top with marshmallows.
Broil for 1–2 minutes, just until the marshmallows are golden brown. Watch closely to prevent burning!
Finish with Hershey’s chocolate pieces and crushed graham crackers on top.
Let cool slightly, slice, and enjoy!