Drain the liquid from two 400g (14oz) cans of chickpeas into a saucepan. Weigh the pot and make a note of the weight. Simmer over medium-low heat until the liquid is reduced by about half – since you need 150ml (5fl oz) for the recipe it is best to reduce the liquid to just over that. It took about 10-15 minutes for the liquid to reduce, but best check it on a scale periodically as you don't want to end up with too little! Cool completely, transfer to a jar and chill in the fridge overnight or use immediately.
Sift the ground almonds and icing sugar into a large bowl. Pour half the aquafaba into the bowl and mix together vigorously until the mixture forms a paste.
Put the caster sugar and water in a saucepan. Put the rest of the aquafaba in the bowl of your stand mixer.
Bring the sugar to the boil and have your Thermapen handy. When the sugar temperature reaches 110C / 230F start whisking the aquafaba on high speed. Keep checking the sugar with the Thermapen – once it reaches 117 C /242F pour it carefully down the side of your mixing bowl while still whisking on medium speed.
Increase the speed to highest setting and continue whisking for 8-10 minutes till the mixing bowl is cool. You will have a very glossy 'meringue' (unlike egg whites my aquafaba meringue never formed firm peaks both times I made this recipe – this didn't seem to have any adverse effects on the macarons however). Add the colouring paste and mix it in until you have the right colour – best start with a tiny amount and increase if needed.
Add the almond paste to the meringue bowl and mix it together until it's well combined. Don't be afraid to be quite forceful when mixing it and make sure you scrape the bottom and sides of the bowl. The consistency of the batter is very important - it needs to flow smoothly and when dropped back into the bowl it should spread slowly.
Line 4 heavy trays with baking parchment - secure the paper by dotting a bit of macaron batter on each of the tray corners.
Put the batter into a piping bag with a 1 cm / ½-inch plain round nozzle. Pipe small rounds of batter onto the baking parchment, spaced slightly apart as the macarons will spread when cooking. Use a template if you want absolute uniformity or draw circles using a cookie cutter.
Carefully but forcefully knock the trays against your worktop to release any air bubbles. I found the vegan macarons actually were more uniform and had fewer imperfections than the regular kind.
Leave them to dry out for an hour or longer until the tops are touch dry. Humidity and temperature can wreak havoc with this drying time so test them after 30 minutes just to be sure.
Preheat the oven to 120C / 250F. Once the shells are touch dry, bake the trays one at a time for 25-30 minutes, checking them after 20. If your oven tends to have hot spots, rotate the tray halfway through the baking time.
The macarons are ready when they have a smooth, dry top and are firm to the touch. Leave them to cool down completely before carefully lifting off the baking paper.
At this point you can transfer them to a cooling rack and leave them overnight, covered with a clean tea towel. Or store them in the fridge.
Place all the ingredients for the filling in a blender or food processor and blitz until completely smooth. Test for sweetness, transfer to a pipping bag filled with a small round tip and chill until needed.
Pair the macaron shells by size. Carefully pipe the filling around the edge of the shells and then fill the inside. Sandwich together and either serve immediately, or chill in the fridge overnight. This will make the shells softer and give the macarons the right mouthfeel.