French Onion Soup
French onion soup is a rich, sweet and savory broth full of slowly caramelized onions, topped with a toasted baguette and melted Gruyere. It looks fancy but only needs patience, not skill.
- 1 h 35 minTotal time
- 4Servings
- 480kcal / serving
- 22 gProtein
The flavor comes from the onions, so give them the full time. Done right, a pile of sliced onions shrinks to a small, dark, jammy heap that makes the whole pot taste deeply sweet.
The science: why this works
- Slow cooking breaks down the onions and browns their natural sugars, which creates the deep, sweet flavor.
- A little flour cooked in the onions thickens the broth just enough to feel silky.
- Deglazing with wine lifts the browned layer off the pot, and that layer is concentrated flavor.
- A splash of vinegar at the end balances the sweetness so the soup tastes bright and not cloying.
Caramelizing is slow chemistry
Onions are about 90 percent water. As it cooks off, their sugars concentrate and brown through caramelization and Maillard reactions. This takes time. Higher heat only scorches the edges, which is why a steady medium heat and frequent stirring work best.
Learn: Caramelizing onions →Why onions turn sweet
Raw onions taste sharp because of sulfur compounds. Heat breaks those down and releases sugars, so the flavor turns mellow and sweet. Slicing thin and cooking until jammy means more surface area, which makes the transformation faster and more even.
Learn: Why cooked onions turn sweet →French Onion Soup
1 h 35 min · 4 servings · French · Soup
Ingredients
Makes 4 servings
- 4 tbspbutter
- 1 tbspolive oil
- 1 kgyellow onions, thinly sliced
- 1 tspsalt, divided
- 3cloves garlic, minced
- 1 tbspall-purpose flour
- 120 mldry white wine
- 6cups beef broth
- 4sprigs fresh thyme
- 2bay leaves
- 1 tbspsherry vinegar
- ½ tspblack pepper
- 8slices baguette, 1.5 cm thick
- 200 gGruyere cheese, grated
Method
Tips for the best result
- Slice the onions pole to pole so they hold their shape and cook evenly.
- Add a splash of water whenever the bottom of the pot looks dry and the onions start to stick.
- Use real stock or a good broth, since there are few ingredients to hide behind.
Mistakes to avoid
- Rushing the onions on high heat: they burn instead of caramelizing, so keep the heat at medium and stir often.
- Using soggy bread: it dissolves, so toast the baguette until fully dry first.
- Skipping the vinegar: the soup tastes too sweet, so finish with a little acid.
Variations and swaps
- Use a mix of Gruyere and Parmesan for a saltier, nuttier crust.
- Add a tablespoon of brandy or cognac with the wine for deeper flavor.
- Make it vegetarian with mushroom or vegetable broth and a spoonful of miso.
- Swap Gruyere for Swiss or provolone, which melt well but taste milder.
- Swap the white wine for 1/2 cup extra broth plus 1 tsp extra vinegar for an alcohol-free version.
Storing and reheating
Store the soup without the bread and cheese for up to 4 days in the fridge or 3 months in the freezer. Reheat to 165°F (74°C), then add the toast and cheese and broil.
French Onion Soup: questions
How long does it take to caramelize onions for French onion soup?
It takes about 45 to 55 minutes over medium heat. The onions should be deep golden brown, soft and jammy before you add any liquid.
What is the best cheese for French onion soup?
Gruyere is the classic choice because it melts smoothly and has a nutty flavor. Swiss, provolone or a mix with Parmesan also work well.
What kind of onions are best?
Yellow onions are best because they have plenty of sugar and a balanced flavor. Sweet onions work but give a sweeter soup, while red onions can taste muddy.
Can I make French onion soup ahead?
Yes. Make the soup up to 3 days ahead and reheat it, then add the toast and cheese just before serving so the bread stays crisp.
