Name: Slow cooker caramelised onions
Prep time: 5 min
Cook time: 270 min
Total time: 275 min
Ingredients: 4 large onions; 2 tbsp oil; 1/2 tsp sugar; 1/2 tsp salt; 1/2 tsp black pepper; 1/2 tsp dried sage, (oregano or thyme)

Total time: 4 hours 35 minutes

Servings: 4 servings

5 from 2 votes

Jump to Recipe Rate this Recipe

Sweet, melt-in-your-mouth slow cooker caramelised onions that cook low and slow until perfectly caramelised, with no effort from you!

A plateful of caramelised onions on a white plate with a green napkin.

There are several cooking methods that never fail to improve a vegetable: roasting, frying in butter, and caramelising! Onions especially. How could a sweet, soft, caramelised onion be anything less than incredible?

Here's a super easy method for making caramelised onions in the slow cooker - barely any effort required, for an absolutely amazing result!

(and before anyone corrects my spelling... that's how we spell 'caramelized' in the UK!)

A plateful of caramelised onions on a white plate with chunks of mature cheddar.

What are slow cookers good for?

I sometimes see recipes where various ingredients need to be fried in a pan on the hob first, or even cooked in the oven, then assembled in the slow cooker (a lasagne, say), and then slow cooked for 6 hours.

This, to me, seems pointless.

If you're going to go to all the effort of pre-cooking and assembling your dinner anyway, why bother waiting 6 hours for it too? You could probably stick it in the oven for an hour, and end up with a better result.

Instead, I think slow cookers are best for recipes that would otherwise need to bubble away on the stove, or be cooked in a frying pan, for an extended period of time. Using the slow cooker means you still get that low, slow cook, but you don't need to stand there for ages supervising it. Just dump the ingredients in the pot, and leave it to do its thing.

Why use a slow cooker to make caramelised onions?

Anyone can fry up some onions for 10 minutes until they're golden brown and call them caramelised, but true caramelising requires time. You need to cook your onions over a pretty low heat, for a long, long time - that's how you get proper, melt-in-your-mouth, sweet and delicious caramelised onions.

According to Wikipedia, which as we know is the fount of all knowledge, onions need to be cooked for at least 30-45 minutes for true caramelisation to occur. And if you want your onions to caramelise evenly, you need to stir them pretty regularly.

I don't know about you, but standing over the stove for 45 minutes stirring onions doesn't really sound like my idea of a good time.

Slow cooker to the rescue! Just throw in your sliced onions, and the slow cooker will do all the hard work for you, cooking them at a low temperature for however long you choose to leave them. The caramelised onions you see in my main photos took about 4 and a half hours, and I stirred them about twice during that time.

Sliced onions and dried sage in a slow cooker pot.

How to make caramelised onions in the slow cooker

There are very few ingredients in this recipe:

onions, obviously
a little oil
salt and pepper
dried herbs (I used dried sage, but thyme and oregano are both great options too)
a small spoonful of sugar, if you want to help things along a bit

Really, the onions are the only vital ingredient, but the other things just help to make your slow cooker caramelised onions extra tasty.

Lightly caramelised onions partway through cooking, in a slow cooker pot.

Minimal effort

Once your onions are in the slow cooker, you really don't have to do much at all. I stirred mine a couple of times, just to ensure they were cooking evenly (maybe one quick stir every 90 minutes or so!), but that's it.

Your caramelised onions are ready whenever you decide they're ready! The photo above shows my onions after about 2 ½ hours, and the photo below is after 4 ½ hours. How long you leave them will depend on your own preference, and what you intend to use them for.

Caramelised onions in a slow cooker pot.

Uses for caramelised onions

Of course, I'm not expecting you to just dig into a huge pile of caramelised onions for your dinner.

Luckily, there are a million other ways you can enjoy using your slow cooker caramelised onions. Here are a few ideas:

use them as a topping for a vegetarian hot dog or veggie burger
add to a cheesy tart or quiche
pour in some veggie broth and top with a cheese crouton for the perfect French onion soup
scatter them over a homemade pizza
use as a topping for all sorts of canapés (e.g. bruschetta!)
add to scrambled eggs or omelette
combine with cream cheese for a tasty caramelised onion dip
use inside a vegetarian sandwich (especially a grilled cheese!)

What else do you love to use your slow cooker for?