After kilos upon kilos of almond flour that was sacrificed, I will tell you a few things about them.
1. Don't use liquid egg whites
I started turning to boxed liquid egg whites because I don't want to deal with egg yolks. I'm not entirely interested in using egg yolks as the base for my buttercream because the French thinks rich ingredients + more rich ingredients = scrumptious food. Yes, they're right, I'll give them that. But I don't think it crossed their minds that their foods have become so rich and scrumptious even a tiny bite into it will make you full and want to puke because of the richness. No appetite for seconds.
Liquid egg yolks have some funny things in there that will make your macaron batter unpredictable. I've had bone dry batter that wouldn't incorporate back into itself, batter that seems fine but will decide to have hollow body no matter what temperature I bake them at, feet that will grow to Big Foot because the air bubbles in the batter JUST WON'T DIE, uneven rising because the air bubbles in the batter JUST WON'T DIE, feet that will protrude sideways because...you can guess why.
2. Folding...not really
Many recipes says fold the batter to incorporate the shit. Well, sorta not really. I've read on Joe Pastry that you can stir and smear the shit out of it to kill the big air bubbles for about 30 seconds. I've tried it on my last batch, and it does wonders. If your mix doesn't produce a batter in 30 seconds, you're not aggressive enough with it.
After the abuse, I've also taken the advice from some other blog that it should take no more than 50 folding strokes to get the batter to "flow like magma" and to "drizzle like a ribbon" and to "incorporate back into itself within 15-30 seconds". If that doesn't happen in 50 strokes, you're babying it too much. Apparently, the point of making stiff egg whites in the beginning is to obtain the tiny air bubbles in the end that will give you feet. We don't want the large bubbles, so we kill it by being rougher than normal with a whipped batter. Last batch worked like a charm. I used to fold and fold and fold until kingdom come and the ribbons still wouldn't show itself.
3. Double up on the cookie sheets
Just do it. I have what it claims to be "professional grade", it's nice thick and heavy, but it's from Superstore (or for you Easterners "Loblaw") but I will still get maca-wrongs like so
Maca-wrong: too much heat on the bottom - not doubling my cookie sheets
4. Tapping the nipples with a wet finger
It creates a weak spot in the skin/crust that you've wait so patiently to have it form. Besides, if you have mixed your batter to the right consistency, you wouldn't need to do this because the nipples would've fallen back into the batter and become not noticeable. Otherwise, your maca-wrongs will end up looking like this
Weak spot in the crust due to water = foot in mouth syndrome
I call this foot-in-mouth syndrome. It's not great when it happens to people, not good when it happens to macarons either.
5. Italian method don't require aged egg whites or crusting time
It didn't make a darn difference if I aged my eggs or not, so why bother. Crusting is optional too with this method unless you like a thicker crunchy shell and the line between shell and feet is better defined...if you're OCD like that.
6. Get an oven thermometer and a candy thermometer
At least if you failed, you can't blame your oven or your syrup.
For common macarons troubleshooting, see Joe Pastry