Caramelized onions are the reason I don’t trust recipe timings anymore. The first recipe I ever followed said to cook them “until caramelized, about 10 minutes,” so I did exactly that, tipped them onto a burger, and wondered why they tasted like… soft onions. Slightly brown. A bit sweet if I was being generous. Nothing like the dark, sticky, jammy stuff you find in a good French onion soup.
That recipe was just wrong, and so are a lot of others. The real thing takes ages. Once you know what you’re waiting for, though, it’s about the least demanding thing you’ll ever cook.
The ten-minute lie about caramelized onions
Proper caramelized onions take somewhere between 40 minutes and an hour, sometimes longer if you want them really deep. There isn’t a shortcut that gives you the same result, and I’ve tried most of them.
What happens in the pan is slow. The onions gradually lose their water, their natural sugars break down and brown, and the whole lot goes from sharp and crunchy to soft, sweet and almost spreadable. Turn the heat up to rush it and the outsides scorch before any of that has had time to happen. That’s how you end up with onions that are bitter and burnt at the edges but still taste raw in the middle. I’ve made that version plenty of times. It’s not great.
Which onions, and why you need so many
Plain yellow or brown onions are what I use nine times out of ten. They’ve got enough sugar to go properly sweet and enough flavour to stand up to all that cooking. Red onions work too. They just end up a murky purple-brown that looks a bit odd on a plate. White onions are sharper and a little less sweet.
The bit that catches everyone out is the shrinkage. A huge, heaped pan of sliced raw onion cooks down to a small bowlful, maybe less. So whatever amount you think you need, double it. Four or five big onions is my starting point for anything more than one sandwich.
Slice them thin, from the root end to the tip rather than across into rings. Cut that way, the slices hold their shape better and don’t collapse into mush.
Low heat and a wooden spoon
I melt a knob of butter with a splash of oil in my widest heavy pan over a medium heat. The butter’s there for flavour, and the oil stops the butter burning. In go the onions with a good pinch of salt, which pulls the water out and gets them softening faster, and I stir until everything’s coated and glossy.
After ten minutes or so they’ll have slumped right down. That’s when I turn the heat to medium-low and settle in. For the first stretch you hardly need to touch them, just a stir every five minutes or so while you get on with something else. As they get darker they need more attention, because the sugars catch more easily towards the end.
Use the widest pan you own. Piled up in a small one, the onions on the bottom steam in the moisture from the ones on top, and steamed onions don’t brown. You also don’t need to add sugar. It’s a common tip, but onions have plenty of their own, and extra sugar mostly just makes them burn sooner.
The brown stuff on the pan is the good stuff
Partway through, you’ll notice a brown layer building up on the bottom of the pan. The first time I saw it I panicked, because I thought the onions were burning. They weren’t. That layer is concentrated onion flavour, and it’s the best part.
When it gets nicely dark, pour in a small splash of water and scrape it all up with a wooden spoon. It hisses, the water lifts the brown stuff straight off, and it gets stirred back through the onions, making them darker and richer each time. I end up doing this four or five times over a batch. If the layer ever goes black and smells acrid, though, that’s actual burning, and the heat needs to come down.
People sometimes add a tiny pinch of baking soda to speed things up. It does work, but the onions go very soft and lose their shape, so I only bother if they’re going into a soup or a dip that’ll be blended anyway.
Making caramelized onions worth the wait
Since they take this long, I never make a small amount. In a sealed container they last about 4 to 5 days in the fridge.
For longer than that, I spoon them into an ice cube tray, freeze them, then pop the cubes out into a bag. They keep their quality for around three months like that. One cube dropped into a pan sauce or a soup, or stirred through some gravy, adds a sweetness you can’t really get any other way. It feels like cheating.
You can make them in a slow cooker as well. Give them several hours on low with the lid propped slightly open so the steam escapes. They come out a little softer, but it’s almost entirely hands-off.
Caramelized onions at 1 a.m.
This is the real reason I keep a stash in the freezer. Late at night, a couple of cubes of caramelized onions warmed in a pan turn basic food into something good. Pile them into a grilled cheese and it tastes like you made an effort. Spoon some over a fried egg on toast, or stir them into instant noodles with a bit of butter. One hour of slow, easy cooking on a weekend keeps paying off for weeks.