Preheat oven to 350°. Line a 9x13" pan with parchment paper. (Or spray with cooking spray).
Whip the butter and brown sugar until light and fluffy, 3-5 minutes.
Add eggs & vanilla and beat another 30 seconds until well mixed.
In a separate bowl mix the flour, graham cracker crumbs, baking powder and salt.
Mix the wet ingredients with the flour mixture until well mixed.
Press about ⅔ of the mixture onto the bottom of the prepared baking dish.
Drop the marshmallow cream by spoonfuls over the crust.
Cover with chocolate squares or chocolate chips. *Reserve some for the top.
Drop clumps of cookie dough on the top leaving some spots uncovered. Place some broken chocolate (or chocolate chips) on top.
Bake for 30-32 minutes.
Cool completely before cutting into pieces.