1 stick unsalted butter, softened
3/4 cup sugar
1 large egg
1 1/2 teaspoons vanilla extract
1 1/3 cup flour
3/4 cup graham cracker crumbs
1 teaspoon baking powder
1/4 plus 1/8 teaspoon kosher salt
4 (1.5 oz) Hershey's Milk Chocolate Bars
1 (7 oz) jar of Marshmallow Creme/Fluff
Using an electric mixer, beat together the butter and sugar until light and fluffy. Add the egg and vanilla and beat until incorporated, scraping down the sides once. In a separate bowl, mix together the flour, graham cracker crumbs, baking powder, and salt and add to the butter mixture, beating just until incorporated.
Press half of the dough into the bottom of a lightly greased 8x8 or 9x9 pan. Spread the marshmallow creme on top in an even layer and top with an even layer of the chocolate bars (break up as needed to fit). Press the rest of the dough on top and bake for 20-25 minutes in a 350 degree oven.
Remove from oven, let cool, cut into squares and serve!