Preheat oven to 350 and grease an 8 x 8 pan. In a large bowl, combine the butter and both sugars with a mixer. Beat in the egg and vanilla.
In a separate small bowl, combine the flour, graham cracker crumbs, baking powder, and salt. Add this to the butter mixture and mix on low speed until combined.
Divide the dough in half. Press half of the mixture into the bottom of the prepared pan. Lay the chocolate bars on top. 2 king size Hershey bars should fit perfectly, but you can use any size bar, breaking it to fit the pan. Next, layer the marshmallow creme.
Take the remaining graham cracker dough and press it out onto waxed paper. Press it to the size of the 8 x 8 pan. Lift the paper and flip the square of dough onto the top of the creme. Now, you essentially have one great big s'more!
Bake for 30-35 minutes until dough turns golden brown. Let cool completely before cutting into bars.