You will adore this sweet and subtle red onion soup recipe! Soft and smooth sliced red onions in a simple vegetable broth, and of course topped off with that compulsory grilled brie toast!
I am pretty sure that you are all aware of what French onion soup is.
Such a delicious classic, right?
Red Onion?
But in this very next recipe however I use red onions instead of yellow onion this time!
Just for fun really. And also because I just happened to have way more red onions in my pantry than they usual yellow ones.
And what else to serve an onion soup with than a classic cheese toast of course! It is a combo that just works: hearty sweet and soft onions and then that salty melted brie cheese on crunchy bread.
Best Red Onion Soup Recipe with Brie Toast
I like the purple red color that the soup gets because of those smothered and cooked red onions.
That boosts my appetite even more I must say. The fresh thyme, a spoonful of mustard and a the balsamic vinegar are a true flavor explosion as well.
Like I said before I picked up a bag of red onions, quite by accident though. I just realised that when I started to lay out all my groceries at the cashier.
No worries, I was not going to run back to the vegetable department and replace them. I am sure that I can come up with plenty of ideas to use those red onions up!
Red Onion Confit
How about my red onion confit with red wine for instance?
It is a lovely homemade topping for goat cheese and even tacos!
Do you need another recipe for more inspiration?
Then you should also check out my oven roasted red onions, the perfect make ahead side dish for Thanksgiving or Christmas!
In the meantime do try out this red onion soup recipe. It is a lovely treat on a cold autumn day. So let’s get this recipe started.
Dig in before someone else does!
Enjoy!
Best Red Onion Soup Recipe with Brie Toast

You will love this sweet and subtle red onion soup!
- 1 ½ lb red onions (675 g)
- 2 large garlic cloves
- 1 tsp strong mustard
- 3 cups chicken or vegetable stock (720 ml), warm
- 5 sprigs fresh thyme
- 2 tbsp unsalted butter
- 4 slices French bread
- 4 slices brie
- 2 tbsp balsamic vinegar
- pepper
- salt
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Peel the red onions and garlic. Then slice both roughly. Add half of the butter to a large saucepan together with the chopped garlic.
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Place the pan over high heat until the butter has melt. Stir and cook the garlic for 3 minutes. Then add the sliced red onions and the fresh thyme sprigs.
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Stir well and cook the onions for 3 minutes. Then pour in the warm stock. Season the onion soup with a dash of pepper.
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Stir and bring it to a light simmer. Then put a lid on the pan and cook the soup for 5 minutes. After that pour in the balsamic vinegar. Also stir in the mustard.
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Cook for 2 more minutes. Then check the seasoning and add extra pepper, salt, mustard or balsamic vinegar to taste. Take the pan off the heat and let it rest for now. Place the slices of French bread on a baking tray and top with the brie. Sprinkle with a little pepper and salt. Place the tray under a hot grill for 2 minutes or until the cheese has nicely melted. Remove the cheese toasts from the grill. Scoop the warm onion soup into bowls and top with the toast. Serve hot.
Great soup. Maybe put the amount of balsamic in the ingredients list?