You Have to Make and Freeze a Whole Bunch of Caramelized Onions.
Properly caramelized onions—deep, sweet, and soft—can’t be rushed. You can cheat with a little sugar and baking soda , but if you’re a purist, you’ll be hanging around that pot for at least 45 minutes , maybe more. While you’re there, you can make a lot and freeze the leftovers. No one in the history of cooking has cooked too many caramelized onions. It’s much more likely that you’ve watched in dismay as a giant onion turns into half a cup of sweet, sticky slices or chunks and then thought, “Damn it. I should have done more.” And you should have done more. You must always do more. Any time you catch yourself making caramelized onions—for dips, eggs, or burgers—you should at least double, if not quadruple, the amount. Aim for an absurd amount of caramelized onions, then freeze anything you can’t manage to eat in one sitting.
Caramelized onions freeze beautifully and you should take advantage of that. Imagine a life where you can add deep, sweet umami to soups, stews, stews, burgers, and everything else in a quick trip to the freezer. Don’t you want it for yourself? Don’t you want to access a light taste?
How to Freeze Caramelized Onions
There are several ways to freeze caramelized onions. Some people use an ice cube tray, but an onion ice cube is a tiny amount. A cake tin is much more suitable: just line the tin with plastic wrap, crush an onion in it, then cover with another layer of plastic wrap and place the entire tray in the freezer. Once they have hardened, take the frozen onion pucks out of the mold and store them in a freezer bag (freezer).
If you don’t have a muffin tin (or are currently using one to bake muffins), you can also freeze the onions directly in the freezer bag. Inflate the bag, spreading it as you go and pushing out as much air as possible. This helps prevent ice crystals from forming, and freezing the onions as a thin sheet, rather than a block, makes it easier to break them off just the way you want them. (Want to make this even easier? Use a chopstick or pencil to draw portion lines.)
When you’re ready to use the frozen onions, toss the frozen pucks or sheets directly into the simmering liquid, or melt them in a non-stick skillet over low heat until hot, then spread them on burgers or toss them into sauces. This will likely increase your consumption of caramelized onions a lot, which I think you really deserve.