Preheat oven to 350°Line a 9-inch square baking pan with parchment paper or aluminum foil, leaving an overhang on the sides to lift the finished Smores Bars out.
Take 12 graham cracker sheets and crush in a bag or food processor until crumb form. This will make 1 1/2 cups total. For the remaining 4 cracker sheets, break into small pieces for topping, set aside.
Mix together the dry ingredients: flour, graham cracker crumbs, baking powder, baking soda, and salt. Set aside.
In a separate bowl or mixer, blend the melted butter, brown sugar, and vanilla together until combined. Add egg and mix well.
Slowly add in the dry ingredients and stir or mix together. The batter will be thick. Spread evenly into prepared baking pan using a rubber spatula (dipped in water if needed).
Make a layer on top using the chocolate bars to cover. Scatter the remaining broken graham crackers pieces on top of chocolate and bake for 15 minutes.
Remove from oven and scatter marshmallows on top. Pop back into the oven for an additional 5 minutes or until marshmallows are a golden brown.
Remove from oven and allow to cool for 30 minutes. Cut into 12 bars.