In the mixing bowl, whisk the egg whites until loose. Sieve the flour and cocoa. Coarsely grind the chocolate. Add the melted butter, hazelnut meal, powdered sugar, cocoa and chocolate bits. Blend until homogenous.
Place the whole hazelnuts on an oven rack and roast them for 10 minutes. Line parchment paper in the cases of the muffin pan. Fill the cases with the dough. Scatter roasted hazelnuts on top.
Cook for 25 minutes at 390°F (200°C th. 6-7) and let cool down before tasting.