Preheat your oven to 350°F (175°C). Spread the hazelnuts evenly on a baking sheet and roast for about 10 minutes, stirring halfway through, until golden and fragrant. Cool and chop them.

In a large mixing bowl, beat together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes. Mix in the egg and vanilla extract until fully incorporated. Sift in the flour, cocoa powder, baking powder, and salt, then fold in the chopped hazelnuts.

Scoop portions of the dough and roll them into balls, then flatten each ball into a disc. Place them on a lined baking tray with enough space between.

Bake the cookie discs for 10-12 minutes until edges are set and centers are soft. Allow to cool completely on a wire rack.

Melt the dark chocolate in a microwave-safe bowl. Stir in the coconut oil. Dip half of each cookie in chocolate and press reserved chopped hazelnuts on top before it sets.

Allow chocolate to set for 30 minutes at room temperature or refrigerate for 10 minutes before serving.