1. Preheat oven to 350°F (177°C) and line an 8 or 9 inch square baking pan with parchment paper, leaving overhang for easy removal.

2. Cream softened butter and brown sugar together with a mixer until smooth and fluffy, about 3 minutes.

3. Mix in the egg and vanilla extract until fully combined, scraping the bowl if needed.

4. In a separate bowl combine flour, graham cracker crumbs, baking powder, and salt.

5. Add the dry ingredients to the wet mixture and mix until a sticky dough forms.

6. Press roughly two thirds of the dough into the prepared pan to create a thin base layer.

7. Spread marshmallow creme evenly over the dough layer.

8. Sprinkle chocolate chips evenly across the marshmallow layer.

9. Flatten portions of the remaining dough and place them across the top of the chocolate layer, leaving small gaps where the filling shows through.

10. Bake for 25 to 30 minutes until the top becomes lightly golden.

11. Cool completely in the pan on a rack, then lift out using parchment and cut into squares.