1 cup butter, at room temperature
1 teaspoon vanilla extract
3 tablespoons cocoa powder
4 cups powdered sugar
1 cup Nutella
4 tablespoons water or milk (plus more to thin as needed)
crushed toasted hazelnuts (optional)
Using an electric mixer, beat the butter and vanilla until smooth. Add the cocoa powder and powdered sugar and mix on the lowest speed at first (be careful because if you mix it to fast right away, the powdered sugar will just fly in your face, on the counter, on the floor, all over your kitchen in a powdery white mess - trust me... I've done it a thousand times and still haven't learned my lesson).
Add the water and Nutella and mix until smooth and creamy. You may need to add extra water or milk to get the creamy texture.
Use a pastry bag with a large star tip or a spatula to frost a chocolate cupcake (or a two dozen). Sprinkle with crushed toasted hazelnuts if desired. This recipe makes enough to generously frost about 24 cupcakes.