Preheat oven to 350°F. Grease an 8-inch square baking pan.
In a large bowl, cream together butter and sugar until light. Beat in egg and vanilla.
In a small bowl, whisk together flour, graham cracker crumbs, baking powder and salt.
Add to butter mixture and mix at a low speed until combined. Divide dough in half and press half of dough into an even layer on the bottom of the prepared pan.
Place chocolate bars over dough. 2 king-sized Hershey’s bars should fit perfectly side by side, but break the chocolate (if necessary) to get it to fit in a single layer no more than 1/4 inch thick.
Spread chocolate with marshmallow creme or fluff.
Place remaining dough in a single layer on top of the fluff (most easily achieved by flattening the dough into small shingles and laying them together).
