Cooking onions over a low flame for an extended period in order to cause the natural sugars to caramelize is something I do pretty regularly… at least once in any given week at least. Mostly, I do this on an ad hoc basis for a particular meal… as a topping for a steak, for example… but you can also do up a larger batch for keeping in the fridge, or freezer, and thus have then on hand for whenever the need arises.
In the above picture, you can see the end product of processing two large Spanish Onions. It may strike you that these are considerably lighter than the very dark, almost mahogany coloured versions you may have come across (and this is usually closer to how I would cook them for a single use), but for keeping, I find it best to stop the process before the onions lose their integrity and get too dark. That way, you can take a little at a time and, if you like, finish the process quickly by reheating… say, for putting on a burger… or you can simply add them as is to a stew, or sauce, or what have you… Anyway, the process is fairly simple…
Here, you can see that I have popped out the central ‘bulb’ of the onion before slicing. This is not especially important… I have just done it because it makes it easier to cut uniform pieces, and because I will be adding the central portion to the jar of pickled onions I have sitting in my kitchen window.
You can cut the onions vertically into thin slivers (which I often do for a single use), or you can cut half rings, as shown here. I like the longer pieces and it is also important to keep the pieces fairly thick so they maintain their basic shape. If sliced too thinly, they tend to form a ‘jam’.
Once sliced, I like to toss the onion with a little salt and let the pieces wilt a little.
You want to cook your onions over a low to low-medium heat. One can use just oil for this, but a little butter added to this improves the flavour. The amounts of each are not critical, but, basically, you want enough to ensure all the onion pieces are well coated.
Add the onions to the fat once ready, and then sweat the onions, with the pan covered, until they have thrown off a good deal of liquid. Then you can remove the lid and keep cooking. Depending on how much onion you have in the pan, you will want to stir occasionally so that the cooking process happens evenly.
You can make caramelized onions with nothing other than the onion, cooking fat, and salt, but a little liquid of one sort or another will help immensely. Even just a bit of water works, but beef or chicken stock, or wine are also frequently added. Some people use Balsamic Vinegar for a very definite flavour boost, but my favourite addition is stock along with a little dry sherry. You don’t need a lot… a half-cup to one cup in all for this amount of onion is fine… and you just add it a bit at a time to keep things softening nicely and to infuse further flavour, and… as we’ll see next, to preserve the ‘fond’.
Here, the onions are just about finished. If you look to the right side of the picture, you can see a brown residue (the fond) forming on the bottom of the pan. As for making pan gravy, you want to use a little liquid to dissolve this by scraping with a spatula or spoon, and then stir it all in to the onions. Often, after using chicken stock earlier on, I would use a splash or two of Sherry to achieve this but, alas, I had none on hand for this occasion… No matter, though. I will be saving this batch and can add Sherry later.
Anyway, you will see that there is a considerable difference in volume between the large bowl of fresh onion slices and the finished product in the first picture. You can, of course make a much larger amount but, for best results, use a pan that is sufficiently wide that you aren’t piling the onion more than a few inches deep.
I forgot to take a picture, but the first use of this batch was later that same day. I pan-fried a small, very thick steak and then, as the steak rested, I quickly sautéed some of the onion in the pan-juices, deglazing with just a splash of Tawny Port. I then used this as a bed for the steak after it was sliced. The whole process of finishing the onions took no more than a minute.