Method: Sift the almond powder and confectioners' sugar. Add the cocoa powder. If necessary, use a food processor for a few seconds if the mixture is not fine enough. Whisk the egg whites, sugar and egg white powder until firm. Fold the dry mix into the egg whites. Fold until the mixture becomes shiny and somewhat loose (you should have to squeeze the mixture from the piping bag, not let it run). This process is called macaronner. Pipe 90 1-in. diameter disks onto parchment paper and let rest for about 30 minutes until they form a skin. Bake in a 300°F (150°C) convection oven for 2 minutes with the vent closed and 8 to 9 minutes vent open. Let cool and freeze immediately. Yields 45 sandwich cookies.