Preheat the oven to 350°F. Line a 9x9-inch baking pan with parchment paper, leaving some overhang on the sides for easy removal.

In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated sugar until well combined. Add the egg and vanilla extract and whisk until smooth.

Add the flour, baking soda, and salt. Fold with a spatula until a cookie dough forms. Avoid overmixing.

Fold the chocolate chips into the cookie dough until evenly distributed.

Arrange graham crackers in a single layer across the bottom of the prepared baking pan, breaking them into pieces as needed to cover the surface.

Spread about two-thirds of the cookie dough evenly over the graham cracker layer.

Arrange marshmallows over the cookie dough, spreading them into an even layer.

Drop small pieces of the remaining cookie dough over the marshmallows. It’s okay if some marshmallows peek through.

Bake for approximately 25 minutes, or until the cookie dough is lightly golden and mostly set.

Remove from the oven and immediately scatter Hershey’s chocolate pieces over the top. Gently press them into the warm cookie layer if needed.

Let the bars cool in the pan for at least 30 minutes before slicing. For cleaner cuts, allow them to cool completely.

Enjoy!