Preheat the oven to 350 degrees.  Line a 13x9 baking dish with parchment and set aside.

In the bowl of a stand mixer, combine the softened butter and brown sugar.  Cream until smooth.

Add in the eggs and vanilla and mix until combined.

Add in the flour, graham cracker crumbs, baking powder and salt.  Mix thoroughly, scraping down the sides as needed. Press approximately ⅔ of the dough into the bottom of the prepared pan.

Dollop the marshmallow fluff over the dough and spread slightly.

Place about ⅔ of the chocolate pieces over the marshmallow fluff.

Top with pieces of the remaining dough, leaving some of the marshmallow and chocolate exposed.

Bake in the preheated oven for approximately 30 minutes or until the edges are just beginning to brown.

Remove from the oven and immediately top with the remaining chocolate pieces.  They will melt into place as the bars cool.

Allow to cool to room temperature before cutting.