Sieve the sugar, cacao and ground almonds to obtain a very thin mixture (or you can also use a blender).
Beat the egg whites until stiff. Once they are firm, add 10gr of powdered sugar (2 times 5gr).
Add the eggs to the sugar, cocoa and almonds mixture. Mix it to obtain a smooth dough. Don't over mix it.
Pre heat the oven (150ºC thermostat 5). Using a pastry bag, make some circles on a non-stick griddle. Let it rest in the open air for 20min.
Put the macarons in the oven for 20min.
To prepare the ganache, heat the cream and pour it on the chocolate. Mix and then add the butter. Mix again before saving it in the fridge.
Take the macarons out of the oven and let them cool for a few minutes. Remove them from the griddle, add the ganache and let them in the fridge all night in a Tupperware.