In a mixing bowl, beat egg whites with a hand mixer or stand mixer on medium speed until foamy. Add ½ the granulated sugar and beat on high speed. Add the remaining granulated sugar and continue beating until egg whites reach stiff peaks.
Using a fine mesh sieve, sift together the almond flour, powdered sugar, and cocoa powder into the meringue. Press remaining pieces into the sieve and discard any leftover large pieces.
With a rubber spatula, fold the mixture into the meringue, pressing the batter against the bottom and sides of the bowl and scooping it back together until the batter ribbons off the spatula when lifted. Do not overmix.
Line one or two large baking trays with parchment paper, cut to size so the edges lay flat.
Fill a piping bag fitted with a round tip. Pipe batter onto prepared baking tray into 1 - 1 ½ inch disks.
Lift and drop the baking tray onto a hard surface 2-3 times to smooth out the batter and knock out any air bubbles. Pop any air bubbles that rise with a toothpick.
Allow macarons to rest at room temperature for one hour, until a skin forms on the surface of the macaron.
Preheat oven to 285˚F (140˚C) while you wait.
After an hour, gently brush the top a macaron with your finger to check that a skin has formed. The batter should not stick to your finger, if it does, allow to set for an additional 15 minutes.
Bake macarons for about 15 minutes, or until they cleanly peel away from the parchment when lifted.
Allow the shells to cool completely before filling.