Preheat oven to 350 degrees and grease an 8 in cast iron skillet
In a medium size bowl add ground flaxseed with 1 1/2 tbsp water and let set for 3-5 minutes
Add in the butter and sugar and stir to combine
Fold in flour , baking powder, baking soda, salt, and vanilla until well combined
In the cast iron skillet make a layer of graham crackers in the bottom of the skillet. Break as needed to fit around the bottom (It is okay to have some small holes)
Dollop pieces of the cookie dough around the cast iron skillet and then press in an even layer.
Cook for about 20 minutes until the dough is lightly brown
Remove from the oven and sprinkle on the chocolate chips followed by marshmallows
Place in the oven and turn oven on broil for 1-2 minutes until marshmallows become toasted on the top.
Then ready to serve! If you have any leftovers be sure to reheat to melt the chocolate and marshmallows