Make Macaron Shells:
Process the almond flour and 2 cups of powdered sugar on high, in the food processor for about 3-5 minutes, with breaks to let the mixture cool down in between (overheating the mixture might cause it to turn to paste and release the oils) and to scrape the sides and bottom. Scrape the sides every minute or so.
Whip egg whites in a clean bowl of a mixer. As soon as the egg whites start to gain volume, gradually add 2 tablespoons of powdered sugar. Whip them just until they are firm but still glossy and supple – when you lift the whisk, the whites should form a peak that drops just a little.
Sift the dry ingredients and the cocoa powder through a fairly large holed sieve into the egg whites and gently fold them in, in 2-4 additions. The egg whites will deflate and form a thick batter. Keep folding until the peak from the batter dropped into a bowl disappears in less than 30 seconds. Do not over mix.
Spoon the batter into the pastry bag and pipe 1 inch domes about 2 inches apart, by holding the pastry bag ½ inch above the baking sheet, applying gentle pressure, then releasing the pressure and quickly moving the pastry tip in a swirl motion up.
Once all batter is piped onto the sheets, take a sheet and rap it against the counter as many times as it needs for the domes to spread into about 2 inch circles and for the tops to become smooth (this might take 5-10 times). Dust macarons tops with some more cocoa powder, if you wish.
To make ganache:
Spoon or pipe 1 tsp of ganache onto 1 of the macaron shells, covering it with the other one. Repeat with the rest of the macaron shells. Allow the macarons to sit at room temperature overnight, then transfer to refrigerator until ready to serve.