1. Add the egg, Nutella and vanilla extract to a large bowl and mix on high speed for about 2-3 minutes until well combined. Add the flour and mix until just combined. Place the dough in the fridge for about 15-20 minutes.

2. Preheat the oven to 180°C (350°F). Line a baking sheet with baking parchment. Fill the Nutella in a piping bag and set aside. Chop the hazelnuts coarsely.

3. Take the dough out of the fridge and divide it into twenty pieces and shape them into balls. Place on the baking sheet and make a well in the middle of each ball (works best with your fingers or the end of a wooden spoon). Pipe some Nutella in each hole and sprinkle with the hazelnuts. Bake the cookies for about 10-12 minutes. Take them out of the oven and let them cool down on the baking sheet for some time, then transfer to a wire rack and let them cool down completely. Store in an airtight container.