Baking these cookies is as enjoyable as eating them. Here’s how you can make them at home:

1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
3. In a large bowl, cream the butter, granulated sugar, and brown sugar until light and fluffy, about 3-4 minutes.
4. Add the egg and vanilla extract to the butter mixture and mix until well combined.
5. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
6. Fold in the chopped hazelnuts, ensuring they are evenly distributed throughout the dough.
7. Using a tablespoon or cookie scoop, portion out the dough onto the prepared baking sheet, spacing them about 2 inches apart.
8. Make a small indent in the center of each dough ball and fill with about a teaspoon of chocolate hazelnut spread.
9. Carefully fold the dough around the spread to seal it inside, then roll the dough into a ball again.
10. Bake in the preheated oven for 10-12 minutes until the edges are set but the centers are still soft.
11. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

From my experience, the key to these cookies is not overbaking them. The gooey center is what makes the magic happen, so keep an eye on them and trust the process!