Slow Cooker Caramelized Onions

Ginny McMeans

Published:

March 2, 2019

Last Modified:

July 22, 2025

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Caramelized Onions have that natural sweet-savory flavor that quickly turns any meal into something extraordinary. And with the help of a slow cooker, you can make them ahead of time and have them at hand for any weeknight recipe.

a bowl of golden brown caramelized onions

Do you love caramelized onions? I do and on almost everything.

But it takes about an hour to make on a stovetop to truly caramelize onions until they are perfectly golden-brown and completely tender. Not sautéd but rich, sweet and caramelized.

The onions need to cook slowly over low heat until they release their sugars and their color turns a beautiful walnut brown. Most of us don’t have that time when preparing meals during the week.

That is why the crockpot is so great for this handy how-to. It does all the work for us. You slice the onions, load them into the slow cooker, turn the settings on low and go on with your life.

I usually make a huge batch so that I always have these mouthwatering onions on hand. You really should too. It’s so easy.

They freeze beautifully but I recommend freezing leftovers in different sized containers or freezer jars so that they can serve as either a last-minute topping or as a larger side to complement your dish.

After defrosting from the freezer they taste just like freshly prepared slow cooker caramelized onions.

I’ll bet you don’t need any inspiration for adding these flavor-packed onions to your menu. But you might love some of these ideas.

Is there a perfect kind of onion to caramelize?

No matter what type of onion you choose, here are a couple of things to consider:

Onions with low moisture content are best. White onions tend to be drier and spicier and therefore an excellent choice to caramelize.
When you slow cook them over an extended period, their natural sugars caramelize, and they have this intensely delicious flavor with a nice tender bite to them.
Yellow onions often have a milder flavor than white onions. They still caramelize nicely and keep that tender texture. Try to choose large all-purpose yellow onions that are firmer.
I would be more reluctant to choose sweet onions (like Spanish yellow onions) as they have a higher moisture content.
Sometimes Spanish sweet onions can result in more loss of sugar and therefore less flavor with a more mushier texture. I would recommend using these types of onions more in their raw state like on salads instead of in this recipe.
Red onions are definitely on the sweeter side than yellow or white onions. If you adore them, then, by all means, caramelize them. You should know though that they can turn out more grayish or with an almost brownish-burgundy color.

But in the end, any onion will caramelize, and I suggest not to be shy. Experiment.

It is all about individual flavor. I prefer either white or yellow onions. White is my favorite.

In any case, I often choose large onions. It is faster to prep a big white onion than several small onions.

What Can Slow Cooker Caramelized Onions Be Used With?

Last week some went into our soup, and it took this already delicious warm dish to a whole new level.
I enjoy them with so many kinds of sandwiches and love them on bean burgers.
They are great as a pizza topping, and you should try them with my Vegan Veggie White Pizza, I used 1/4 pint of frozen caramelized onions that I took out of the freezer the night before. It was terrific!
I need to slip this information in for the white pizza too. You know what else you need? Homemade Vegan White Pizza Sauce!
Use them to add an incredibly deep flavor to your favorite plates of pasta, lentil and rice dishes. And yes, even sweet potatoes!
Try not to stand over the crockpot eating them by the forkful. Good stuff!

The list is endless.

This recipe is so simple and delicious that you have to try it!

The only thing left is for you to get onions caramelized so that you can enjoy them all of the time.

Step-by-Step Instructions

Slice onions. Peel and thinly slice your onions until you end up with about 5 quarts total.
Prepare slow cooker. Brush olive oil (you can also use coconut or your favorite cooking oil) around the bottom and about halfway up the sides of the inside of the slow cooker. I used a 6 quart crock pot here, but any 4 to 6 quart size cooker will work.
Add onions. Fill up your slow cooker with the sliced onions. Mine came up about ¾ full, but it’s okay if yours is even more full as the onions will start to cook down very quickly. Turn the heat to low, cover, and cook for 10 hours.
Stir during the last hour. Stir the onions a few times during the last hour of cooking to make sure they are browning evenly and to encourage a deeper color.

Ready to serve! After 10 hours your slow cooker onions should have a lovely golden brown color and be tender and sweet. Enjoy them as a side dish to your main course or use them as an ingredient in other recipes like I mentioned above!

How To Store

Refrigerating – Let your cooked onions cool, then pack them into an airtight container and refrigerate for up to 4 days.

Freezing – Again, allow them to cool first before storing. I recommend freezing your onions in ice cube trays or even muffin tins, that way you can remove as much as you need at any time without having to defrost a huge block of them. Once frozen, you can remove the frozen clumps of onions from the ice trays or muffin tins and transfer them to freezer bags.

Thawing – Transfer to the fridge the night before you plan to use them.

Reheating – If you would like to warm the onions, you can pop them in the microwave for 15 second increments, stirring in between until hot. Or, reheat your caramelized onions in a small pot over low-medium heat.