1. Beat the butter, brown sugar, and granulated sugar together until light and fluffy.

2. Add the egg and vanilla extract, mixing well.

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

4. Gradually combine the dry ingredients with the wet mixture until a dough forms.

5. Cover and chill the dough in the refrigerator for 30 minutes.

6. Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.

7. Scoop dough into balls and place on the sheet.

8. Bake for 9–11 minutes or until edges are firm and centers slightly soft.

9. Let cookies cool completely.

10. Dip each cooled cookie halfway into melted chocolate.

11. Sprinkle with chopped hazelnuts and drizzle remaining chocolate on top.

12. Let set at room temperature or chill briefly until the chocolate firms.