In a 9×9 inch baking pan, spray with non-stick cooking spray. Set aside.

In a large non-stick pot over medium heat, melt butter. Add in marshmallows and stir together with butter and Nutella until marshmallows have melted and become creamy. Stir in vanilla extract.

Fold in Cocoa Krispie cereal until all marshmallows and cereal are evenly mixed together. Spread treats into sprayed baking pan. Press into pan. Place into fridge for 10 minutes to cool.

Slice into bars and serve. Devour.