2king-sized Hershey's milk chocolate bars(if you want a more subtle chocolate flavor use regular sized chocolate bars; enough to fit)
1 1/2cupsmarshmallow creme/fluff(7 1/2 oz jar)
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. This part can be tricky. I made little disks with the dough and formed them into a sheet on some parchment paper then transferred it over. Spread it around gently. You can also roll the top dough layer in between two sheets of plastic wrap until it's in a square then placed it on top.
Bake for 25 to 35 minutes, until lightly browned. Cool completely before cutting into bars. Makes 16 cookie bars. These are great warmed up in the microwave for 10-15 seconds.