Preheat the oven to 350 degrees. Prepare your brownie pan.

In a pan over low heat, melt the butter. Stir in the cocoa until incorporated.

Add the sugar and remove from heat.

Mix in the eggs and vanilla extract.

Add the flour a little at a time and mix well.

Add the chocolate chips.

Pour into prepared brownie pan.

Drop the marshmallow fluff in heaping spoonfuls. Use a knife to swirl it throughout the brownie batter.

Bake in a 350 degree oven for 20-25 minutes or until toothpick inserted in the brownie comes out clean.