Slow Cooker French Onion Soup
Let your appliance do all the hard work to make this spectacular slow cooker French onion soup! It’s rich and flavourful, and topped with a giant cheesy crouton.
If you like it when your dinner cooks itself, you’ll love this slow cooker French onion soup. It’s rich and earthy, sweet and tangy, and all-round wonderful. Add a super cheesy crouton, and you may as well just marry it now.
Slow cooker soup
I’m so excited to get my slow cooker out of the cupboard, now that the weather’s cooling off. There’s nothing better than an appliance that takes a job off my hands (notable mention to my other best buddy, the dishwasher).
A slow cooker is the perfect low effort appliance. Just chuck in a few raw ingredients (which in this case literally took me about 8 minutes), leave it to cook throughout the day, and dinner’s made itself. Hurrah!
Soup is the perfect thing to make in a slow cooker, as whatever you add has plenty of time to cook down beautifully, intensifying the flavours. Often, the amount of time you cook soup for isn’t hugely important, so if you’re not quite ready to eat when the soup’s ready, it probably won’t mind simmering away for another hour or two, until you’re hungry.
What is French onion soup?
This time, I used my slow cooker to make French onion soup. If you’ve never had French onion soup before, you can probably guess what it is: an onion soup that originated in France, way back in the 18th century.
French onion soup is incredible. It’s a brothy soup, with plenty of pieces of soft, sweet caramelised onions throughout. The broth is intensely flavourful – sweet and earthy in equal measures.
And best of all… French onion soup is often served with a thick, gooey, cheesy crouton. Just in case you thought it couldn’t get any more wonderful.
How to make slow cooker French onion soup
Step 1: Add the soup ingredients to the slow cooker
Before I get too carried away with that cheesy crouton, we need to make the actual soup. Obviously the main ingredient is onions, but there are a few other ingredients to add to the slow cooker too, which all combine to make a seriously tasty broth:
- garlic
- vegetable stock
- dried thyme
- black pepper
- balsamic vinegar
- a little sugar
- butter
It all melts together, along with the juices from the onions, and creates an incredible soup.
Step 2: Cook low and slow
Give everything a good mix, and leave it to cook in the slow cooker. I prepared my soup after breakfast, and it was ready to eat by dinner time – about 9 hours. The long cooking time gave the onions a beautiful deep brown colour, and really intensified their flavour.
If you don’t have as much time on your hands, it will be fine to eat after about 6-7 hours, but it won’t be quite as rich in colour or flavour.
You can eat French onion soup on its own (which is still really tasty!) – if that’s what you’d like to do, you’re already done. Seriously easy, right?
However, I’d highly recommend doing one more thing…
Step 3: Make the cheesy crouton
The enormous, cheesy crouton that you often find on top of a bowlful of French onion soup is the perfect way to finish off the recipe.
The underside of the crouton soaks up a little of the broth, while the top is covered with a blanket of gooey melted cheese.
Traditionally, the crouton is grilled right on top of the soup. As long as your bowl is heat-safe (don’t use a plastic bowl, for example!), you can heap the bread and cheese right on top, and stick it straight under the grill (broiler).
I’d recommend allowing the grated cheese to cascade down over the side of the piece of bread, rather than being too tidy with it… the end result is like an avalanche of molten cheese that pools in the soup and makes it extra yummy.
What cheese should you use for French onion soup?
Traditionally, the crouton on a bowl of French onion soup uses French cheese – usually either Comté or Gruyère.
To be honest though, I don’t like buying expensive ingredients that I only need for one recipe – so I just used a bit of good old cheddar instead. It’s very hard to go wrong with a cheesy crouton, so it really won’t matter.
Just use whatever cheese you have on hand. It’ll be tasty whatever you go for.
What if I don’t have any heat-safe bowls?
No problem! If your bowl won’t survive under the grill, just cook the cheesy croutons on a baking tray instead, then pop them on top of a hot bowl of soup. You won’t get quite the same effect, with the cheese overflowing into the soup, but it will still be delicious.
Can I cook French onion soup in advance?
Yep! This slow cooker French onion soup reheats really nicely, so feel free to cook it in advance of when you need it. I know not everyone has 9 hours to spare before they want to eat each day!
To reheat, you can either bring the whole batch to a simmer in a pan on the stove, or microwave one bowlful at a time. Don’t add the cheesy crouton until right before you’re ready to eat, otherwise it will get too soggy underneath.
Slow Cooker French Onion Soup
If you’ve cooked this recipe, don’t forget to leave a star rating!
Print Pin CommentIngredients
For the slow cooker French onion soup:
- 4 large onions sliced
- 30 g (~ 2 tbsp) butter, roughly chopped
- 1 tbsp caster sugar (optional)
- 1 tbsp balsamic vinegar
- 2 tsp minced garlic or garlic puree
- 1 tsp dried thyme
- 1 tsp black pepper
- 750 ml (~ 3 cups) vegetable stock
For the cheesy crouton:
- 2-4 thick slices French baguette
- 2-4 tbsp grated cheese (I used cheddar)
Instructions
- Add all of the soup ingredients to a slow cooker, and mix well to break up the onions. Cook on high for approximately 9 hours, or until the onions are a deep, rich brown colour, and very soft.
- Serve on its own, or with a cheesy crouton. To make the cheesy crouton, dish up a bowlful of soup into a heat-safe bowl, and top with 1 or 2 thick slices of French baguette. Sprinkle over plenty of grated cheese, then place under a grill (broiler) for a few minutes, until the cheese is melted and slightly crispy. Serve immediately.
Nutrition
Nutritional information is approximate, and will depend on your exact ingredients. Please calculate your own nutritional values if you require accuracy for health reasons.
Love using your slow cooker? Check out this collection of more vegetarian slow cooker recipes:
Last night I made a French Onion Soup for the first time and I was rather underwhelmed. The flavor combination of this one seems spot on and I can’t wait to try it! Just hand wrote it on a card and filed it in my recipe box – I’m a bit old-fashioned in that way.
What kind of beer do you like using best for this recipe?
Hi Megan, I just use a standard pale lager but to be honest I think most things would work – a darker beer will just give you a darker, stronger tasting soup :)
Can I use anything else? I don’t wanna use beer.
You could just use more stock instead :)
OK I posted incorrectly, what is vegetarian beer?
Some beers, e.g. Foster’s and Guinness, use isinglass, which comes from fish’s swim bladders, in the filtering process. Vegetarian beer is beer that uses no animal products at all.
@Becca @ Amuse Your Bouche,
Hello
How much beer do you put in this French Onion Soup? When do you add the beer?
Guinness is now Vegan.
Thank you!
Apologies, the beer was included in an older version of the recipe. I left it out of my updated version as I didn’t feel it was necessary. But if you’d like to include it, just add a cupful of dark beer at the start of cooking.
25 grams is equal to 2 tablespoons:)
Yep that sounds about right! :)
just wondering… what is vegetarian beer?
Just one question….how much is 25g of butter in terms of tablespoons.
So funny, I just made French Onion Soup for my hubby yesterday! It’s like his favorite soup, but I still only make it a couple times a year. I love the idea of making it in a crockpot though, that would make things much simpler!
i love french onion, i always buy a veggie version from trader joes, but this looks amazing! the boyfriend loves it too, id love to make him eat a vegetarian version!
I bought those le creuset bowls with the handle just to enjoy French onion soup. Love it!
French Onion soup is one of my all time favorites and this definitely seems like a great recipe. Seems like a really simple recipe as well, thanks for sharing :)
Happy Blogging!
Happy Valley Chow