Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper for easy cleanup later.

Place hazelnuts in a dry pan over medium heat. Toast for about 8 to 10 minutes, shaking the pan occasionally to avoid burning them. Once fragrant, transfer to a bowl to cool, then chop coarsely.

In a large bowl, use an electric mixer to cream the softened butter and sugar together for 2 to 3 minutes until the mixture is light and fluffy.

Beat in the egg and vanilla extract, mixing until smooth.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt until well combined.

Gradually add the dry mixture to the wet mixture, folding gently until just combined. Be careful not to overmix; a few lumps are okay!

Gently fold in the chopped hazelnuts and chocolate chips until evenly distributed throughout the dough.

Use a tablespoon or cookie scoop to drop rounded balls of dough onto the prepared baking sheet, keeping them about 2 inches apart.

Place in the oven and bake for 10 to 12 minutes. The edges will be set while the centers will remain a little soft.

Once done, cool the cookies on the baking sheet for about 3 to 4 minutes before transferring them to a wire rack to cool completely.