Preheat oven to 350 degrees and spray a 9 x 13 inch baking pan with non stick spray and line the bottom with parchment paper.
In a mixer fitted with a paddle attachment, combine melted butter and brown sugar. Mix until combined.
Add eggs and vanilla extract. Mix until the batter is smooth.
Add flour and stir until just combined. Do not over mix.
Stir in chopped graham crackers, marshmallows and chocolate chips.
Spread batter into the prepared pan and bake for 25-30 minutes, or until the edges have turned a golden brown.
Allow the bars to cool before cutting.