In a large nonstick pot, melt the butter over medium heat.

Add in the marshmallows, and stir until smooth and melted. Remove from heat, and stir in the cereal.

Mix everything together until evenly coated, then stir in the Nutella until just mixed.

Spray a 9x13 pan with nonstick spray, pour in the rice krispie treats, and press down into an even layer. Allow to cool completely.

If desired, drizzle additional Nutella on top for decoration. Slice and serve!