Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking pan lightly with cooking spray or line it with parchment paper.

In a large mixing bowl, cream the softened unsalted butter, brown sugar, and granulated sugar for about 2-3 minutes, until light and fluffy.

Add the large eggs one at a time, mixing well after each addition, then pour in the vanilla extract and blend until fully incorporated.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add this to the wet ingredients, mixing gently until just combined.

Fold in the graham cracker crumbs and chocolate chips carefully using a spatula, ensuring they are evenly distributed throughout the dough.

Spread half of the cookie dough evenly into the prepared baking pan, pressing gently to create a smooth layer.

Sprinkle mini marshmallows generously over the dough layer, then dollop remaining cookie dough over the marshmallows, spreading it to cover them.

Sprinkle extra chocolate chips and marshmallows on top for added gooeyness.

Bake for 25-30 minutes until golden brown. A toothpick inserted should come out clean with a few crumbs.

Cool the bars in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

Once cooled, slice into squares and enjoy.