To Make The Cupcakes:

1. In the bowl of an electric stand mixer, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Add in vanilla.
2. In a separate bowl, whisk together the flour, cocoa, baking soda and salt until combined. Then in an additional separate bowl, stir together buttermilk and coffee. Add dry ingredients to creamed butter mixture alternately with buttermilk and coffee, beating well after each addition.
3. Line baking pans with about 24 paper baking cups, and fill each two-thirds full with batter. (Here is my tutorial for filling cupcake liners.) Bake at 375° for 15-20 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.
4. Once the cupcakes have reached room temperature, use a melon baller (or a small spoon) to scoop out a small portion from the middle of the cupcake (about 1 teaspoon). Fill the empty space with a teaspoon or so of Nutella. Then top the cupcakes with the Nutella frosting (recipe instructions below.)

To Make The Nutella Frosting:

1. Using an electric mixer, cream butter and Nutella together on medium-speed until smooth. Add in vanilla and beat until smooth. Reduce speed to low and gradually add powdered sugar until incorporated. Add milk until you reach the desired consistency** (see note below), then increase speed to medium-high and beat for 1 more minute. Pipe or spread onto cupcakes, or cover and refrigerate in a tightly-sealed container for future use.
2. **If your buttercream is too thick, add more milk/cream. If it is too thin, add more powdered sugar.