Grease an 8x8 inch baking pan; preheat ove to 350°.
Cream together butter and sugar with an electric mixer until smooth; beat in egg and vanilla.
In a separate bowl, whisk together flour, graham cracker crumbs, baking powder, and salt. Add the dry mixture to the wet mixture and mix on low speed till combined.
Divide the dough in half, spreading half of it on the bottom of the pan and leaving the rest in the fridge for later use.
Place the chocolate bars on the dough to cover the dough; spread the marshmallow creme over the chocolate.
Place remaining dough in a single layer on top of the marshmallow by forming it into an 8-inch square on parchment paper. Turn upside down on the marshmallow layer and peel off the paper. You may need to press the dough around to cover the marshmallow.
Bake for 30-35 minutes, or until top turns a golden brown. Allow to cool completely before cutting. I recommend making these the day before you need them so they can cool all the way.
Cut into squares and serve. Enjoy!