Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.

Toast the hazelnuts in a dry skillet over medium heat for 8-10 minutes. Once fragrant, rub them in a towel to remove loose skins and coarsely chop.

In a large bowl, beat the softened butter and sugar until light and fluffy, about 2-3 minutes.

Add the egg and vanilla extract to the mixing bowl and beat until smooth and glossy.

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

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Fold in the chopped hazelnuts and chocolate chips by hand, keeping larger pieces for texture.

Drop rounded tablespoons of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10–12 minutes. The edges will be set, while the centers remain slightly soft.

Let the cookies cool on the baking sheet for 3-4 minutes, then transfer to a wire rack to cool completely.