Preheat oven to 350 degrees Line a 9X13-inch pan with parchment paper, leaving a 2-inch overhang. Grease the parchment paper with nonstick cooking spray and set aside.
In a medium bowl, whisk together the flour, graham cracker crumbs, baking powder and salt.
In the bowl of a stand mixer, beat the butter and brown sugar until light and fluffy, about 2 minutes. Beat in the eggs and vanilla until well combined.
Add the dry ingredients and mix on low until just combined.
Divide the dough in half. Press half into the bottom of the prepared pan until the dough is evenly flattened.
Dollop the marshmallow creme on top of the cookie dough base and spread into an even layer with a spatula.
Place the peanut butter in a small microwave safe bowl and heat for 30 seconds. Stir the peanut butter and drizzle over the marshmallow topping. Place the peanut butter cups, in rows, over the marshmallow topping and peanut butter.
Gently flatten and press the remaining dough over the top of the peanut butter cups, doing your best to cover most of the peanut butter cups.
Bake the bars until golden brown, about 32 to 37 minutes. It is ok if some of the marshmallow puffs up outside of the bars. It will settle as it cools. Cool the bars completely. Remove from the pan with the parchment paper. Cut the bars into squares and enjoy!