Preheat the oven to 350 degrees F. Line an 8 inch square metal pan with nonstick foil.
Mix the graham cracker crumbs with the sugar and melted butter. Press into bottom of lined pan and bake for 8 minutes.Prepare brownies. Melt the chocolate and butter together in the microwave, a double boiler or heavy saucepan. Set aside to cool for about 5 minutes. Meanwhile, whisk the eggs and sugar until light.
Whisk in the vanilla, then whisk in the salt and baking powder.
Add the melted chocolate to the egg mixture and stir until mixed.
Add flour and stir until mixed. Do not overbeat, just stir until it’s absorbed.
Pour the brownie mixture over the graham crust. Return to oven and bake for 22-26 minutes or until set.
Remove from oven and sprinkle marshmallows over top in one generous layer. Set oven’s broiler heat to high and return pan to oven. Broil for 1 minute or until golden. Keep a close eye, because marshmallows brown quickly!
Let cool on a rack. When cool, chill. Lift from pan and cut into 9 big squares.Makes 9 large brownies