Preheat oven to 375°.
Line a 13x9 inch baking dish with parchment paper.
Using a food processor, or a gallon size Ziplock bag and a rolling pin, crush 2 cups of graham cracker crumbs.
In a large bowl mix 2 cups of graham cracker crumbs, 2 cups of flour, ½ cup of granulated sugar, ½ tsp. baking powder, and ½ tsp. salt.
Slowly add in 1½ sticks of melted butter to graham cracker mixture. Mix until large clumps form.
Press graham cracker mixture into the bottom of 13x9 inch parchment paper lined baking dish.
Bake for 15-18 min. or until golden brown.
While crust is baking cut chocolate into ½ squares.
Remove crust from oven.
Preheat oven to broil.
Spread all but 1 cup of chocolate chunks over hot graham cracker crust.
Once the chocolate chunks have melted, spread evenly over the graham cracker crust.
Let stand for 5 min.
Sprinkle marshmallow over the chocolate.
Sprinkle remaining chocolate chunks over the marshmallows.
Place bars in oven until toasted to a golden brown. Approximately 1-2 mins.
Remove from oven.
Let stand for 15 mins.
Cut and ENJOY!!