01 -
Preheat oven to 350°F. Line an 8-inch or 9-inch square baking pan with parchment paper, leaving overhang for easy removal.
02 -
In a large bowl with a handheld or stand mixer fitted with a paddle attachment, cream butter and brown sugar on medium-high speed for about 2 minutes until light and creamy. Add egg and vanilla extract, mixing until fully incorporated. Scrape down the bowl as needed.
03 -
Whisk together flour, graham cracker crumbs, baking powder, and salt in a medium bowl.
04 -
Pour the flour mixture into the creamed mixture and beat on medium speed until combined. The dough will be sticky.
05 -
Press or spread two-thirds of the cookie dough into the prepared pan, forming a thin, even layer.
06 -
Spread the marshmallow creme evenly over the cookie dough base. Gently work to achieve an even layer as much as possible.
07 -
Scatter the chocolate chips evenly over the marshmallow creme layer.
08 -
Flatten remaining dough into pieces and arrange over the chocolate chips. Some filling will remain exposed.
09 -
Bake for 25–30 minutes or until the top is lightly golden brown. Remove pan to a wire rack and cool completely.
10 -
Lift cooled bars from pan using parchment overhang. Cut into squares. Store leftover bars in an airtight container at room temperature for up to 1 week.