Preheat your oven to 350°F (175°C). Spread the hazelnuts on a baking sheet and roast for about 10 minutes. Once cooled, rub off the skins and chop.

In a large bowl, cream softened butter with granulated and brown sugar until light and fluffy, about 3-4 minutes. Add eggs one at a time, mixing well after each addition.

Sift flour, cocoa powder, baking powder, and salt into the mixture and fold gently. Incorporate the chopped hazelnuts carefully.

Scoop dough and roll into balls, then flatten to form discs about an inch thick. Place on a parchment-lined baking sheet.

Bake the cookies for 10-12 minutes until edges are set and centers remain soft. Cool on the baking sheet before transferring to a wire rack.

Melt dark chocolate in a microwave-safe bowl using 30-second bursts, stirring until smooth. Stir in coconut oil, if desired.

Dip each cooled cookie halfway into the melted chocolate and press hazelnut pieces on top. Let cool until chocolate hardens.