It’s hard to improve on caramelised onions. When you need so little to make something so delicious, why even try? Fair enough — but you can make them even better with a quick marinade.
Marinades do more than enhance the flavour of a dish — they’re also an initial cooking step. Salt, sugar, and acid break down the cell structure of proteins and vegetables and draw out some of their water content, both of which tend to make food more tender. This is exactly what happens when you marinate onions. Because they’re already partially cooked, they’ll soften a bit faster — and if your marinade contains any amount of sugar, they’ll brown faster, too. This does mean you’ll have to watch them more closely, but the tradeoff is turbo-speed caramelised onions.
There’s no wrong way to marinate onions, so the possibilities are endless. Any leftover vinaigrette you have will work very nicely, as will a simple 1-2-3 punch of soy sauce, mirin, and miso. Pickling liquid absolutely counts as a marinade, too: Whether you keep it classic, spice things up, or opt for a beer-based brine, pickled onions caramelize beautifully and quickly. You can treat caramelised pickled onions like a shortcut to onion jam heaven — they’re already cooked (more or less), so they don’t need much encouraging to collapse into a sticky, jammy, delicious mess.
You don’t need to concoct a whole marinade. Just a bit of salt, sugar, and (optionally) oil will drastically alter the texture and flavour of onions. I don’t cook meat at home anymore, but when I did, my favourite move for stews and braises was dry brining the meat overnight with a truckload of sliced onions, salt, brown sugar, and smashed garlic cloves. This method practically candies the onions in meat juices and brine, which makes them even more melt-in-your-mouth tender and delicious than you ever thought possible.