In the bowl of a stand mixer fitted with a paddle attachment, or with a hand mixer, beat the butter and cream cheese on high until fluffy (about 3 minutes). Using a rubber spatula, scrape down the sides of the bowl. Turn the mixer to low and add in the powdered sugar, 1 cup at a time. Mix on low until combined. Add the Nutella and mix on high until the frosting is completely smooth. If adding, stir in the meringue powder and mix until fully combined.