Preheat oven to 350 degrees and line a 9x9 or 11x7 baking dish with non-stick foil or grease well with baking spray. (The 9x9 pan will yield thicker bars while the 11x7 will be slightly thinner. The ones pictured above were made in a 9x9 pan.)

In a bowl, cream butter, brown sugar, and granulated sugar together until well combined.

Add in eggs, one at a time, beating well after each addition.

Add in vanilla extract and mix.

Next, add in baking soda, salt, all purpose flour, and cocoa powder. Mix until well combined.

Lastly, add in chocolate chips and chopped oreo cookies and mix until combined.

Spread half of the cookie dough evenly in the bottom of the pan.

Spread marshmallow fluff on top of the dough as evenly as possible.

Press or spread the remaining cookie dough on top of the marshmallow fluff in an even layer (it’s fine if some of the marshmallow fluff is showing).

Bake for about 25 minutes, or until the cookie bars have risen and the center is not jiggly when the pan is moved gently.

Allow to cool at least 30 minutes before slicing. I prefer waiting at least an hour before cutting into them, or even refrigerating them and then cutting into them. By the way, these taste fantastic cold!

Store remaining bars in an airtight container. They are fine at room temperature, if it’s not too warm, for 3-4 days. Or, you can refrigerate them as well.

Enjoy!