Using a stand mixer with whisk attachment (or a large bowl and regular mixer), beat butter 1 minute on medium-high speed.
Add Nutella and cream for another minute on medium-high speed.
Add powdered sugar and mix until combined. It will look very powdery and won't be frosting consistency yet.
Add 1ablespoon T milk while the mixer is running. Add milk ½ Tablespoon at a time, mixing thoroughly after each addition, until desired consistency is reached.
Use this frosting to frost cupcakes or brownies, make graham cracker sandwiches, stuff strawberries or raspberries...the possibilities are endless!