Preheat oven to 150C (300F). Line 2-3 baking trays with baking paper or a silpat and put aside.
Place almond meal and icing sugar in a food processor and pulse to get a finer consistency. Sieve the mixture into a large mixing bowl and set aside.
Divide egg whites in two batches, each 75 (2.6 oz) grams. Place one batch of egg whites in an electric mixer fitted with a whisk attachment, add cream of tartar and egg white powder (if using) and set aside.
Mix the remaining egg whites with a metal spoon into the almond/sugar mix to make a thick paste, then set aside.
Put sugar and water in a saucepan on medium/low heat and stir until the sugar is dissolved. Dispense with the spoon and put up the temperature to moderate heat. Insert thermometer.
When thermometer reaches 110C (230F), start whisking egg whites on low speed. Gradually increase the speed until the egg whites are thick. (If the sugar syrup gets too hot before the egg whites are ready, add three teaspoons of cold water to syrup to reduce the temperature). When sugar syrup reaches 118C (244F) and the egg whites are ready, slowly pour syrup down the side of the mixer (aim for the edge where the whites touch the side of the bowl) while whisking the egg whites on medium speed (don’t worry about the sugar splattering and hardening on the sides – this is quite normal).
Continue to mix for 7-10 minutes until the meringue cools (the bowl should still feel slightly warm).
Using a firm spatula, mix half of the meringue into the almond meal paste – you don’t need to be careful – you’re really just loosening the mixture. Add the remaining meringue and fold using a ‘fold-pat down’ motion through the middle of the mixture (I flatten the mixture around the sides of the bowl as I go to deflate the air somewhat in the mixture – this helps to avoid hollow, soft macarons). Take the mixture to a lava-like consistency where it drops slowly but steadily off the spatula (you want to be able to create an unbroken figure 8 shape) forming a ribbon of mixture which slowly oozes into the mixture (don’t overmix though; better to slightly undermix).
Place a large piping back into a heavy vase or jug (for stability), folding down a good sized ‘collar’ at the top of the bag. Pour or spoon the mixture into the bag (use a half inch nozzle). Hold the piping bag vertical over the tray about an inch and pipe the mixture out in one ‘dollop’ rather than a circular motion. Keep a good space between each mixture, as it will flatten out a little. Depending on the size of your trays, you’ll need 2-3.
Once done, rap trays a few times on the bench firmly to bring any bubbles to the surface (this prevents cracking) and then pop any remaining bubbles with a toothpick.
As soon as you’ve piped the cookies, put the first tray into the oven and bake for about 16-18 minutes. At about 16 minutes, open the oven and check whether they’re done – very lightly touch the top edge of a macaron – if it’s still wobbly or the feet compress, give it another minute or two. They’re done when they feel firm and the feet themselves don’t compress when they are lightly touched.
Remove the tray from oven and cool completely on a wire rack (don’t try taking off the cookie until they’re cool), then repeat until all the trays are cooked.
When cool, remove the cookies from the trays. If making ahead, these can be stored in a sealed container in the pantry or in the fridge (particularly if you have high humidity) until ready to fill.