Age(!) the eggs whites in a container either in the fridge for 24 - 48hrs in advance or heat gently in a microwave on a medium-low for bursts of 10 seconds or so, to get that 'aging'
process. This is to dry out the egg whites to prevent the mixture getting too wet as this can cause the cracks. Its supposed to make a huge difference apparently. I just put them in an oven for a few minutes to dry out.
Whisk the egg whites to soft peaks, not like meringues just yet, but just foamy. Add the sugar gradually beating continuously till it gets glossy and shiny, like a meringue. Add the vanilla extract.
In a large separate bowl, mix together the icing sugar and ground almonds and sieve to remove all lumps, this will give the macarons that smooth texture. Umm, I don't have a sieve so I skipped this section, big mistake.
Macaronage stage:
Add half the almond/icing sugar mixture into the egg whites. Fold in gently for around 20-25 strokes. Add the rest of the almond/sugar mixture and vanilla and fold for another 20-25 strokes. So, I don't know, but apparently you only know when it's ready with experience but the mixture should look like lava and it should take no more than around 50 folds. I think I over did it, nevermind, I have learnt now.
Scoop mixture into a piping bag and pipe on to lined cookie trays into roughly 1 inch circles. Tap the trays on to the tabletop a couple of times to get the bubbles to come to the surface and pop them. Leave the trays of piped cookies to air for 30-60 minutes for the shells to form skins (this will help the cookies get the highly sought after feet).
Bake at 150 C or gas mark 3 for 10-12 minutes. Cool completely before piping buttercream and making into sandwiches. Put into an airtight container in the fridge overnight to mature before eating. Its supposed to improve the flavour and allow the macarons to absorb some moisture from the filling to get the perfect chewy texture. But i couldn't wait that long.