Line 2 baking trays with baking paper and place a template underneath baking paper, if using. Fit a piping bag with a medium round nozzle and set aside.
Place the ground almonds and icing sugar into a food processor. Pulse 10 times, then sift into a large bowl, discarding any large lumps that do not go through the sieve. Repeat this process once more.
Add one of the 36g portions of egg white to the almond/sugar mixture. Mix well to make a paste, then set aside.
Place the remaining 36g of egg white into the clean metal bowl of a stand mixer, fitted with the whisk attachment. Set aside.
Place the caster sugar into a small saucepan with 30ml of water. Place over a medium heat and start to bring to a boil. Do not stir- swirl gently if necessary.
When the sugar syrup has reached 114°C, turn stand mixer to high speed and begin to whip egg whites to soft peaks.
When the sugar syrup has reached 118°C and the egg whites have reached soft peaks, with mixer still on high, pour the sugar syrup down the side of the bowl in a slow, steady stream. Once all of the syrup has been added, turn the mixer up to full speed and beat for 5 minutes, until stiff peaks are reached. Meringue will be ready when the bowl comes to room temperature.
When the meringue is ready, add 1/3 of it to the almond paste. Mix vigorously to combine fully and loosen the thick paste.
Add the rest of the meringue and fold, using a figure of eight motion, until mixture is cohesive and comes off the spatula in ribbons- if you leave those ribbons for 30 seconds, they should level themselves out into the rest of the mixture.
Place the macaron mixture into the piping bag. Holding the bag vertical to the baking tray, pipe macarons about 4cm in diameter, leaving plenty of space between each one.
Once macarons are piped, lift the whole tray up, and drop down on the work surface a few times to raise any air bubbles to the surface. Use a sharp knife/cocktail stick to burst any bubbles, letting the mixture fall back onto itself.
Set the macarons aside at room temperature to form a skin- on a relatively dry day, this should take about 30-40 minutes, but can take less time on drier, warmer days and more time on cold, humid days. Check on the macarons every 10-15 minutes or so, if unsure. The macarons will be ready when you can gently touch the surface without any batter coming off on your finger.
When the macarons are almost ready, preheat the oven to 165°C fan. Bake the macarons in the centre of the oven, one tray at a time, for 11 minutes. To check if they are done, place a finger on top of the shells and wiggle gently. When done, the tops of the macarons should not wobble. Remove from the oven and allow to cool completely on the tray.