(If using a box mix, prepare the batter according to the directions on the back of the box--I suggest Ghirardelli boxed brownie mix or Betty Crocker).
Over a double broiler, or in the microwave, melt butter and chocolate together. Once melted, allow to cool about 10 minutes.
Next, add in the sugar, and mix. Add in eggs, one at a time, stirring after each addition. Next, add in vanilla.
Add in espresso powder, salt, baking powder, flour, and cocoa powder. Mix until just combined.
Add in oil and chocolate chips, stir.
Pour 2/3 of the batter into the baking pan. Sprinkle 1 cup of marshmallows evenly over the batter. Top the marshmallows with the rest of the batter, doing your best to cover all the marshmallows with batter.
Bake for 25-30 minutes, or until brownies are no longer wet in the middle.
Pull the brownies out of the oven and top with graham cracker pieces and chopped chocolate.
Bake for 1 minute.
Allow the brownies to cool and enjoy!