1 1/2 cups butter (3 sticks), at room temp
3 cups powdered sugar
2 t vanilla
1 cup Nutella
Cream the butter in the bowl of stand mixer fitted with the whisk attachment, about 5 minutes. Add the powdered sugar and mix, gradually increasing in speed, until the sugar is fully incorporated. Add the vanilla and whisk until the mixture is light and fluffy, about 5 minutes; you may need to stop the mixer and scrape down the sides of the bowl a couple times.
When the buttercream is fluffy, add the Nutella. Whisk for another 5-8 minutes until the Nutella is fully incorporated and the buttercream is light and fluffy again.