Bistro French Onion Soup
There’s something about a bowl of French onion soup that always feels like a treat. The melted cheese, the golden bread, the rich onion broth. It is cozy and elegant all at once.
This is my husband’s favorite soup, and it’s one of those recipes that seems fancy but is surprisingly simple once you know the rhythm. With just a few ingredients and a little patience, you can make something that tastes restaurant-worthy in your own kitchen.
This version follows my 7-Step Soup Method, which breaks every soup into clear building blocks: fat, flavor base, liquid, protein, mix-ins, spices, and finishes. Once you understand those steps, you can tweak it to your taste. Make it lighter with vegetable broth, richer with extra butter, or top it with your favorite cheese.
However you serve it, this soup always feels special.
✨ Pin this recipe for later so you have it handy, and be sure to check out my other soup recipes if you’re building your soup-making skills!
Bistro French Onion Soup
Ingredients
- 4 tbsp butter
- 3 medium-sized onions (thinly slices)
- 1 tbps sugar
- 1 tbsp flour (optional, for a thicker broth)
- 4 cups beef broth
- 2 tbsp beef bouillon (optional)
- 1 tbsp balsamic vinegar or dry sherry (optional)
- 1 tsp fresh thyme (or ½ tsp dried thyme)
- salt & pepper (to taste)
- 2 croissants (sliced or torn into pieces)
- 1 cup Swiss or Gruyére cheese (shredded)
Instructions
Fat
- Melt butter in a large Dutch oven or soup pot over medium heat.
Flavor Base
- Add sliced onions, sugar, and salt. Cook slowly, stirring often, for 25–30 minutes, until deep golden brown and caramelized. If the onions start to stick, add a splash of water and scrape up the browned bits.
Liquid Base
- Sprinkle flour over the onions (if using) and stir for 1 minute. Add balsamic vinegar or sherry, then pour in the broth and add the bouillon. Add thyme and pepper. Simmer uncovered for 20 minutes to develop rich flavor.
Protein
- Optional – this soup is delicious as-is, with the onions as the main star.
Mix-ins
- Optional – the onions from the base and the crouton and cheese finishes add body.
Spices
- Taste and adjust seasoning with salt, black pepper, and thyme as needed.
Finishes
- Slice or tear croissants into pieces. Arrange on a baking sheet, top with shredded Swiss, and toast at 400°F for 5–7 minutes until golden and crisp. Ladle soup into bowls and top with cheesy croissant croutons. Garnish with fresh thyme before serving.
Notes
- For a deeper flavor, add a splash of balsamic vinegar or dry sherry while the soup simmers.
- If you love rosemary, a very small sprig or a few leaves can be beautiful here. Just use it lightly, as rosemary can quickly take over the flavor.
- Croissants make a lovely stand-in for traditional baguette croutons — buttery, crisp, and perfect for soaking up the rich broth. Any kind of bread could be used here though.
This Bistro French Onion Soup is proof that comfort food doesn’t have to be complicated. A few slow-cooked onions and a handful of pantry staples turn into something deeply satisfying and perfect for lunch on a chilly day or a cozy dinner for two.
If you make it, I’d love to hear how it turned out for you. Share your favorite toppings or tweaks in the comments below, and don’t forget to save the recipe on Pinterest so it’s easy to find next time you’re craving something warm and homemade.
✨ Looking for more cozy inspiration? Visit the 7-Step Soup Collection for simple, comforting recipes you can make anytime.
