Grease an 8 x 8 glass baking dish with butter and set aside.

In a large pot on very low heat add the butter, Nutella and marshmallows. Stir together until melted and smooth. 

Take off heat, stir in vanilla and salt, mix to combine.

Gently stir in Rice Krispie cereal until combined, pour into glass baking dish and spread out evenly. 

Let sit on the counter until cooled and firm, about 30 min. Cut into squares and enjoy.