These slow cooker caramelized onions are unbelievably easy to make, and only require 2 main ingredients!
- 3–4 pounds white, yellow or red onions, peeled and thinly sliced
- 3 tablespoons butter (or olive oil), melted
- salt and pepper
- optional: 1 tablespoon of brown sugar and 2 teaspoons of balsamic vinegar
- Add onions to the bowl of your slow cooker. Drizzle the melted butter evenly over the top of them, then toss with a spoon (or with your hands) until the onions are evenly coated in the butter.
- Cook on low for 8-10 hours, stirring once or twice if desired, until the onions are a rich golden brown and caramelized. Season with salt and pepper (and brown sugar and/or balsamic, if desired), and stir to combine.
- If your onions are really juicy at this point, set the lid an inch or so ajar. If they are not, leave the lid on regularly to seal in the moisture. Then continue cooking the onions for an additional 3-4 hours until most of the extra liquid has evaporated and the onions are a deep golden brown, and thick and “jammy”.
- Serve the onions immediately, or cover and refrigerate for up to 3 days. Or freeze for up to 3 months.
Lid Ajar: The onions will definitely release lots of natural juices while cooking, which can make the onions slightly soupy near the end. So if you would like that liquid to evaporate, thus making your onions a little thicker and “jammier”, just set the slow cooker lid slightly ajar (1-inch of so) for the final few hours of cooking.
Balsamic and Brown Sugar: I happen to fall in the camp of believing that caramelized onions are plenty flavorful on their own. But if you taste them in the final few hours and decide that they need some extra flavor, just stir in some balsamic vinegar and brown sugar to taste. They will provide the extra savory and sweetness that many people love.
Know Your Slow Cooker: These onions should be able to cook unattended for 10+ hours without any babysitting or stirring. (Although I do recommend stirring them once or twice if you can.) But that said, every slow cooker is different. And the low heat setting on yours could be hotter than most. So, as is good common sense with any slow cooking, I just recommend keeping watch especially during your first batch to be sure that the onions do not burn on the bottom.