Preheat oven to 350°F. Spray an 8-inch square baking pan with PAM. In a large bowl, cream the butter and sugar. Add the egg and vanilla. In a separate bowl, combine the flour, graham cracker crumbs, baking powder and salt. Add to butter mixture and mix until well 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. Spread chocolate with marshmallow creme or fluff. Place remaining dough in a single layer on top of the fluff.
Bake for 30 to 35 minutes, until lightly browned.
Recipe by Five Wooden Spoons at https://www.fivewoodenspoons.com/2012/11/21/smore-bars/