1.5 kg white, yellow or red onions, peeled and thinly sliced
3 tbsp butter (or olive oil), melted
salt and pepper
1 tbsp brown sugar
2 tsp 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), 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. 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.
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.
