1. whisk eggs and sugar together in a bowl. 2. Add in the melted butter and whisk again. 3. Add in the sour cream, followed by the coffee. 4. Sift in the dry ingredients, and scoop the mixture into a muffin tray with 12 paper muffin forms attached till they are almost filled up. 5. Bake in oven for 25-30 minutes at 180°c (check if they’re done with a toothpick). 6. Let them cool down completely at room temp before filling them with nutella, and piping with frosting. 7. Make small holes in the cupcakes (with the back of a piping tip, and fill the cupcakes with nutella. 8. Pipe a circle around the cupcakes and press it into the chopped roasted hazelnuts. 9. Then pipe a swirl on top of the circle and decorate with a ferrero rocher.