In a large mixing bowl, begin to whisk the egg whites until bubbles start to form. Slowly add the sugar in additions, whisking well after each addition. Continue whisking the meringue until stiff peaks form.
If your ground almonds are quite wet or doesn't seem to be very fine you can quickly blitz them with the icing sugar in a food processor on the pulse setting for a few seconds. Regardless if you took this last step or not, you need to sieve the icing sugar and ground almonds a total of three times. This is to remove any lumps and any larger pieces of ground almonds.
Add in the ground almond and icing sugar mix in two goes. Very carefully fold this into the egg whites, being mindful to avoid knocking out the air initially. About 10 folds per addition such be sufficient for now.
Next, add in any food colouring if using and fold another 15-20 times. The mix should be at the "ribbon stage" (when you drop the mix off the spoon, it should fold in on itself still briefly). If you think the macaron mix is still a little too thick, wait 20-30 seconds before folding more, and only fold another 5-6 times and reassess. It's much better to under mix these than over mix.
Next, transfer this mix to a large piping bag fitted with a 1mm round tip. Or just cut the bag very carefully to achieve a perfectly straight line that will result in a perfectly piped circle. (No pressure)
Line your baking sheets with parchment paper and pipe your macarons with plenty of space in between each one. You can use a macaron template for this, simply place the macaron mat directly onto your baking tray, put a layer of parchment over it, pipe your macarons and then slide the mat out from underneath.
Bang the trays of macarons sharply down onto your counter to bust any large air bubbles left and to level them off to create a smooth surface.
Place your trays in the driest part of your kitchen and rest the macarons for anywhere between 30 minutes to 4 hours depending on how humid your kitchen is. You're looking for the top to form a slight skin, you should be able to run your finger over them without sticking.
20 minutes before your macarons are ready to bake, preheat your oven to 150°c (300°f).
Place one (yes you have to bake one at a time, I'm sorry) tray in the sweet spot of your oven, In most ovens, this is the lower third of your oven.
Bake for 22 minutes total, but after 5 minutes turn the oven temperature down to 140°c or 280°f. Halfway through baking, very quickly open the oven to turn them around and close quickly.
Allow to cool totally before removing from the tray.