Use a sieve to sift cocoa powder, icing sugar, and cornstarch together into a large bowl.
Add the ground nuts and salt.
Stir the amaretto or extract into the egg whites. Add most of the egg white mixture to the dry ingredients, until a thick, firm batter is formed. If the batter is too dry, continue to add the remaining egg whites.
Dip a small ice cream scoop into the bowl of icing sugar reserved for decorating and then scoop the batter onto the lined baking sheets. This will cover the dough in the sugar to create that snow-capped finish to your cookies. It also helps prevent the batter from sticking to the ice cream scoop!