Preheat the oven to 350°F/180°C or 160°C fan oven, and line a 9x13 (approx. 23×33 cm) baking pan with parchment paper. Lightly grease it with cooking spray and set aside.
In a large mixing bowl, mix together the flour, graham cracker crumbs, baking soda, baking powder, and salt. Set aside.
In the bowl of a stand mixer, cream the butter and both sugars until smooth and fully combined. Then add the eggs and vanilla extract and continue to beat until just incorporated.
Gradually add the dry ingredients and beat on medium speed until there are only minimal streaks of flour in the dough.
Fold in 1 cup of chocolate chips until evenly mixed in.
Using your fingers, press about ¾ of the cookie dough into the bottom of the parchment lined baking pan. Break apart half the amount of Hershey’s bars and evenly layer it on top.
Spread the marshmallow creme on top and then sprinkle with the remaining chocolate chips.
Take pieces of the remaining cookie dough and flatten it out with your hands then place the pieces in a single layer on top of the chocolate chips, leaving small gaps for the marshmallows to pop out.
Bake for 25 minutes. Remove from the oven and top with the remaining pieces of Hershey’s bars, mini marshmallows, and chocolate chips. Then bake for an additional 10-15 minutes or until the edges are lightly browned and the top part of the cookie looks set.
Allow the bars to cool in the baking pan on a wire rack at room temperature for 30 minutes to an hour.
Cut into 12 squares and serve.