Classic French Onion Soup
A deeply savory, soul-warming soup built on a foundation of slowly caramelized onions in a rich beefy broth, finished with a crusty bread cap and a blanket of melted Gruyère cheese. This bistro classic transforms humble onions into something luxurious with patience and a hot broiler.
For 4 servings
- prep
Slice the onions.
Halve the onions through the root, peel them, and slice them thinly into half-moons, about 1/8-inch thick. You should have roughly 8 cups of sliced onions.
TIPUse a sharp knife or mandoline for even slices — even thickness means even caramelization. - saute · ~50 min
Caramelize the onions.
1.In a heavy-bottomed pot, melt butter with olive oil over medium heat.2.Add all the sliced onions and stir to coat them in the fat.3.Cook for 15 minutes, stirring occasionally, until the onions soften and release their liquid.4.Stir in the sugar and continue cooking for 30–35 minutes, scraping the bottom of the pot frequently, until the onions turn a deep mahogany brown.TIPDon't rush this step. The deep brown color is where all the flavor lives. If the onions start to burn, lower the heat and add a splash of water to deglaze. - saute · ~3 min
Add garlic and flour.
Add the minced garlic to the caramelized onions and cook for 1 minute until fragrant. Sprinkle the flour over the onions, stir well, and cook for another 2 minutes to eliminate the raw flour taste.
- simmer · ~28 min
Deglaze and simmer the soup.
1.Pour in 1 cup of the water and scrape up all the browned bits from the bottom of the pot.2.Add the remaining 5 cups of water, thyme sprigs, and bay leaf.3.Season with salt and black pepper.4.Bring to a boil, then reduce the heat to low and simmer uncovered for 25 minutes. - prep · ~10 min
Toast the baguette slices.
While the soup simmers, preheat the oven to 375°F (190°C). Arrange the baguette slices on a baking sheet and toast for 8–10 minutes until dry and lightly golden on the edges. Set aside.
TIPDay-old bread works best — it's drier and soaks up the soup without disintegrating. - prep · ~1 min
Remove herbs and check seasoning.
Fish out the thyme sprigs and bay leaf from the soup. Taste and adjust salt and pepper if needed.
- assemble · ~2 min
Assemble the soup bowls.
Preheat the broiler to high. Ladle the hot soup into oven-safe bowls, leaving about 1 inch of space at the top. Float 2 toasted baguette slices on top of each bowl and pile the grated Gruyère cheese generously over the bread.
TIPPlace the bowls on a baking sheet to catch any cheese that bubbles over — it makes cleanup much easier. - bake · ~4 min
Broil until golden and bubbling.
Slide the baking sheet with the bowls under the broiler. Broil for 3–5 minutes, watching closely, until the cheese is melted, bubbly, and speckled with golden-brown spots.
- serve
Serve immediately.
Let the bowls cool for 2 minutes on the table. Warn everyone that the bowls are extremely hot, then dig in carefully with a spoon through the cheesy crust into the dark, savory soup beneath.
What to keep in mind.
6 tips from the recipe — small details that make a real difference to the final dish.
- 1For deep mahogany color, cook onions low and slow — a pinch of salt at the start helps draw out moisture.
- 2Use a heavy-bottomed pot to prevent scorching during the long caramelization process.
- 3Deglaze the pot with water or broth between stirrings to build layers of flavor from the fond.
- 4Day-old baguette absorbs soup without turning mushy; toast it until completely dry.
- 5Grate Gruyère from a block yourself — pre-shredded cheese contains anti-caking agents that won't melt as smoothly.
- 6Cool leftover soup completely before refrigerating the broth and bread-cheese topping separately to keep the bread from disintegrating.
Adapt it for your goals.
Vegetarian
Substitute the water with a rich vegetable broth made from mushrooms and roasted root vegetables. This delivers a deep umami base without any meat.
beefed upBeefed-up
Use a high-quality homemade or low-sodium beef stock instead of water for a more robust, meaty broth. Add a splash of dry sherry or cognac after deglazing for extra depth.
lighter toppingLighter-topping
Swap Gruyère for a mixture of low-moisture mozzarella and Parmesan for a slightly lighter but still bubbly cheese crust. Or use a vegan melting cheese alternative.
Why this is on our healthy list.
Rich in Quercetin
Onions are a top source of quercetin, a powerful antioxidant that supports heart health and reduces inflammation.
Bone-Supporting Dairy
Gruyère cheese provides calcium and protein, contributing to bone strength and muscle repair.
Low-Calorie Base
The soup is built on water and onions, keeping the base low in calories while delivering substantial flavor.
Frequently asked questions
Heat is too high or your pot is too thin. Lower the heat to medium-low, stir often, and deglaze with a splash of water if the bottom gets dark before the onions are soft.
