8 chocolate Ghirardelli squares or 3 Hershey bars (broken up into squares)
Preheat oven to 350 degrees Fahrenheit
Rub 1 tsp of unsalted butter inside an 8 inch cast iron skillet
In a large mixing bowl, add the granulated sugar, brown sugar, and 1 1/2 sticks of softened butter. Mix with electric mixer until fluffy. Then add eggs, vanilla extract, and mix with electric mixer until combined. Add in the salt, baking powder, and on the low mixing setting slowly add in the flour. Do not add the flour in too much at a time or else the consistency will be affected. Once the flour is fully mixed in, fold in the 1/4 cup of chocolate chips with a spatula. Divide the batter down the center evenly.
Take one half of the cookie dough batter and spread into the cast iron skillet. Using your fingers, press the dough into the bottom to create one even thin layer, form a 1/2 inch wall around the sides. Place the broken in half graham crackers in one even layer, followed by 6 chocolate squares, and 1/2 of the marshmallows. Take the remaining cookie dough and spread over the top, using your hands to create an even layer.
Bake for 25-30 minutes. At the 20 minute mark, remove from the oven and spread the remaining chocolate squares, remaining marshmallows, and sprinkle the graham cracker crumble over the top. Return to the oven to finish baking. If marshmallows are toasted to your liking at the end of cook time, low broil for a few seconds.
Remove from oven and allow to cool for 10 minutes. Serve alone or with vanilla ice cream.