Ingredients :

• Hazelnuts — This is the main ingredient, so don’t go for the cheapest ones. Buy whole hazelnuts to roast yourself — the difference compared to pre-roasted supermarket nuts is huge. In a pan or oven, they develop an aromatic oil that you won’t find anywhere else.
• Cocoa powder — Unsweetened is mandatory. Basic Van Houten works just fine. If you have Dutch-processed cocoa (alkalized, darker), the final color will be even more intense. Avoid sweetened powders like Nesquik — the result would be far too sweet and lacking character.
• Icing sugar — Double role: in the dough as a binder, and as an outer coating for the signature cracked crust. The icing sugar on the surface absorbs moisture from the egg whites during baking, and that is precisely what creates those characteristic fissures.
• Egg whites — They serve as the binder and structure. No need to whip them into peaks — just lightly beaten with a fork to loosen them up. If you have frozen whites lurking in the back of the freezer, this is the perfect time to use them.