I was skeptical about making caramelized onions in the slow cooker. I’d seen lots of blog posts on the method. I’d also read many comments on blogs from people that said they’d tried it, but their onions came out watery or burnt.

I decided to give it a try anyway. I figured the worst that could happen was I’d have to throw away half a dozen onions. I don’t take food waste lightly, but I was willing to take the chance.

I’m pleased to say that caramelizing onions in the slow cooker worked for me. I tossed six, sliced, yellow onions in the slow cooker at 9 p.m. While I slept, they turned into two cups of sweet, soft, tawny-brown caramelized onions. There was one problem — the smell.

I woke up to an overwhelming smell of onions that wasn’t pleasant. When I went downstairs in the morning to check on them, they seemed done enough so I unplugged the slow cooker and put the entire thing on the picnic table out back to cool off. I had to get them out of the house.

Still, the method worked well enough that I would do it again. Next time, I’m going to run an extension cord out to my patio and cook them outside. I’m not kidding. I’ll probably allow them to cook even longer next time, too. The instructions I followed from Shockingly Delicious said to cook them for 10-12 hours. I had mine on for only nine hours before I had to get them out of the house. The flavor from the nine-hour cooking time is very good, but I’m curious to see if it would improve even more if the onions had a couple more hours in the slow cooker.


  • 6 medium-sized, yellow onions
  • 3 tablespoons olive oil
  • non-stick spray


  1. Spray the crock of a 3.5-quart slow cooker with non-stick spray to prevent onions from sticking to sides and burning.
  2. Peel and slice onions into 1/4- to 1/2-inch thick slices.
  3. Add onions to slow cooker and drizzle olive oil over them. Stir to coat evenly.
  4. Place slow cooker on high and cook until onions are caramelized to your taste.

My notes

  • Different slow cookers reach different temperatures. You’ll have to keep an eye on your specific slow cooker to see how long it takes your onions to reach the desired level of caramelization.
  • You could certainly cook more than six onions at a time using this method. The six onions filled the crock of my 3.5-quart slow cooker up about halfway before cooking. I could probably have put three more onions in that slow cooker. Any more, and I would switch to my 5-quart slow cooker. Cooking time for more onions would probably have to be adjusted.
  • Some people add a little salt or some sugar to their onions when caramelizing. I didn’t add those. I wanted to see how they turned out without those things. Next time, I might add a little salt, but I see no need to add sugar. The slow cooking time brings out the natural sugars in the onions just fine.
  • Caramelized onions freeze very well. Divide the finished onions into small, freezer-safe containers, and you’ll have them ready to go when you want them for pizza toppings, burgers, soups, dips, casseroles and more.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.

Slow Cooker Caramelized Onions
Making caramelized onions in the slow cooker is an unbelievably easy way to make a big batch of sweet onions — the perfect addition to pizzas, dips, burgers, so