In the bowl of a stand mixer, cream together the butter and sugar until smooth and creamy.

Add in the eggs and vanilla. Mix well, scraping down the sides often.

Add in the flour, cocoa, baking soda and salt. Mix thoroughly, scraping down the sides as needed.

Fold in the marshmallow fluff just until evenly distributed. Do not overmix.

Using a large ice cream scoop, divide the cookie dough between the baking sheets. Chill the formed dough in the freezer for about 10 minutes just prior to placing in the oven.

Bake in the preheated oven for approximately 10-12 minutes or until the centers are set. Allow to cool