Bake the cakes for about 35 - 40 minutes. Cool the cakes in the pan for 15 minutes then carefully remove the cakes from the pan to cool completely. Once cooled, place the cake layers in the fridge for 1-2 hours before frosting.
Make the Nutella buttercream frosting. Beat the butter and powdered sugar on low speed until smooth and well combined. On low, beat in the Nutella, vanilla extract, salt and 2 tablespoons heavy cream until mostly combined. Increase the speed to medium-high for 1-2 minutes.