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A take on the classic recipe for French Onion Soup but adapted for your Slow Cooker. Complete with giant cheese topped crouton top.

slow cooker French onion soup with cheese crust
There are some recipes that are just begging to be made in the slow cooker, French Onion Soup is one of them. You need to cook the onions slowly for a very long time, using a slow cooker lets you do that without constantly watching a pan. What a win.When you make the traditional version of this soup, it’s also a bit of a faff to put each small bowl into the oven to melt the cheese on top. I decided to go big or go home and make a giant crouton for ease. Just cut it through as you serve the delicious soup underneath.One last thing, you can use ready chopped onions for this to save the crying, but annoyingly, they aren’t quite as good. I timed myself chopping them and it takes about 10 minutes to peel and cut them all (if I’m concentrating and not getting distracted). I think in this case, it might be worth it. Enjoy! 🧅

You’ll love this French Onion Soup recipe because:

✅ So cosy and comforting.

✅ Simple take on a classic.

✅ Just look at that cheese crouton

raw ingredients for french onion soup in slow cooker pan

FAQs about the Slow Cooker French Onion Soup

Which Slow Cooker do you use and recommend?

I use: Morphy Richards Sear & Stew Slow Cooker (it’s light and you can use it for browning on the hob too).

For induction hob users: Lakeland Digital 6.5l Slow Cooker

Also! Top tip, buy a WiFi plug for it so you can switch it on or off from your phone when you’re at work? What a time to be alive.. I have these: Tp Link Tapo Smart Plug (Also you can set up with your Google or Alexa to say “Switch on Slow Cooker” WHATTT 🤯

Can I really leave the onions cooking for that long?

Yes! I sometimes do this on a Friday night so we can have this for lunch on a cosy Saturday.

If I’m making a batch to freeze I just do it during the day when 

Is it safe to leave the slow cooker on that long?

I’m not an electrical safety expert obviously, but slow cookers are designed to cook, well, slowly. It never worries me as this is what they are designed for and I guess it’s just like leaving a light bulb on over night.

Do I have to peel all of those onions though?!

Short answer, no.

You can use pre chopped peeled onions but these tend to come in small pieces rather than strips. This is fine, but if gives the soup a very difference texture and isn’t quite as traditional.

Ideally the onions are cut into strips as they hold their shape better when cooked.

Is this this vegetarian?

There are notes on the recipe but if you substitute the stock for vegetarian and use vegetarian cheese, then, yes.

Can I freeze this recipe?

Yes, you can freeze any leftovers, minus the bread topping. Defrost and reheat thoroughly when you want to enjoy them.

Alternatively, you can freeze all of the ingredients in a bag raw as a ‘dump’ meal and then cook.

Can I prepare this recipe the night before?

Yes. Throw everything for the initial cook into the slow cooker, pop the lid on, then store in the fridge overnight. In the morning put it into the slow cooker and remember to switch on!

close up shot of French onion soup with crispy cheese crust in slow cooker

Fancy more soup recipes?

french onion soup topped with thyme in a black slow cooker

Hope you enjoy this recipe as much as we do. I’d love to know how you got on and what you thought of it if you make this recipe. Please rate the recipe using the ⭐️ by the recipe.

Also, if you’d like to show me a photo by tagging me on Instagram (@tamingtwins) I LOVE to see your creations.

 

5 from 19 votes

French Onion Soup {Easy Slow Cooker Recipe}

A take on the classic recipe for French Onion Soup but adapted for your Slow Cooker. Complete with giant cheese topped crouton top.
Prep Time: 15 minutes
Cook Time: 10 hours 30 minutes
Total Time: 10 hours 45 minutes
Servings: 6

Ingredients 

For the Slow Cook:

  • 1.5 kg Onions, Peeled and cut into strips, see notes.
  • 75 g Butter
  • 3 tsp Brown Sugar
  • 3 tsp Thyme
  • 2 Bay Leaves
  • Salt and freshly ground black pepper

To add to the Onions:

  • 1 litre Beef Stock
  • 100 ml Sherry
  • 2 tbsp Worcestershire sauce

For the topping:

  • Bread Slices
  • Gruyere Cheese

Instructions 

  • Put all of the soup ingredients APART FROM the stock, sherry and Worcestershire sauce into the slow cooker and cook on HIGH for 9 - 10 hours or LOW for 12 - 13 hours, stir occasionally if you are nearby.
  • Remove the bay leaves. Add the stock and sherry and cook for a further 30 minutes. Check for seasoning, it may add more salt.

Optional:

  • Top with the bread slices and cheese and pop under the grill for about 10 minutes to melt.

Notes

Cutting the Onions
You can use ready chopped onions for this to save the crying, but annoyingly, they aren't quite as good. I timed myself chopping them and it takes about 10 minutes to peel and cut them all (if I'm concentrating and not getting distracted). I think in this case, it might be worth it.
Stock
To make this vegetarian feel free to substitute the stock for a vegetarian stock.
Topping
Slices of baguette work well here and Gruyere cheese is traditional as it melts perfectly and the taste is ideal with onions. You can use another cheese if you prefer though.
Nutrition
The nutritional info does not include the topping as we should always measure bread and cheese with our heart!

Nutrition

Calories: 216kcalCarbohydrates: 27gProtein: 3gFat: 10gSaturated Fat: 7gTrans Fat: 1gCholesterol: 27mgSodium: 157mgPotassium: 434mgFiber: 4gSugar: 13gVitamin A: 371IUVitamin C: 21mgCalcium: 74mgIron: 1mg

Nutrition information is automatically calculated, so should only be used as an approximation.

Additional Info

Course: Main Course
Cuisine: French
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5 from 19 votes (17 ratings without comment)

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2 Comments

  1. 5 stars
    Delicious soup! Had a lot of onions to use up & this was perfect. Made without the crouton but will be adding that next time.

  2. 5 stars
    Subtly gorgeous flavours! Such an easy and effective recipe. I fell in love with your site when I read ‘we should always measure bread and cheese with our hearts’. Looking forward to trying more!