Yes, I said crock pot.
I picked up this method from one of the commenters on Serious Eats, and I had to try it to see how it worked.
Sure, it takes a long time in the crock pot, so you have to plan ahead. But after you slice the onions there's not much work until you empty the crock pot. It also makes a large batch, so you'll have plenty to use and more that you can freeze for later use. So you invest some crock pot time and end up with enough onions for several recipes
Another bonus is that if you're watching calories, these pack a lot of flavor with no added fat. The ingredient list is amazingly short. Just onions. No butter, no oil, no water. You can add a pinch of salt, if you want to, but it's just as good to season them when you use them.
Crock Pot Caramelized Onions
Onions, sliced - to fill your crockpot,
No, really. Just onions. That's all you need.
Okay, if you want a pinch of salt, go ahead. But that's all.
Slice the onions 1/4-inch thick or less and pile them into your crock pot. I used a full five-pound bag of onions in my crock pot. Set the temperature to low and let it cook for 24 hours.
Since my crock pot is an odd shape, I checked the onions a few times, and stirred them to make sure they were all cooking evenly.
Here they are when they went into the crock pot:
Here they are after eight hours. They're looking good already:
Here they are after 24 hours:
Depending on how hot your low setting is, you might need to cook the onions a bit longer. You're looking for a dark mahogany brown, with very little moisture. If the onions aren't brown enough, and there's too much liquid, you can turn the heat up to high for another hour or so to cook off the liquid.
And that's it. Onions, done.