Classic French Onion Soup
This is the most rewarding soup you will ever make. Sweet, deeply caramelized onions in a rich, winey beef broth, topped with a thick crouton and a bubbling, golden blanket of Gruyère cheese. It takes patience, but every minute is worth it.
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French onion soup is an exercise in patience that rewards you beyond measure. The foundation — properly caramelized onions — takes a full 45–60 minutes over low heat. You cannot rush this. High heat produces browned-but-not-caramelized onions that taste sharp and acrid rather than sweet and complex. Low and slow is the only way.
When the onions are done correctly, they reduce from a heaping 3 pounds down to about two cups of jammy, deeply sweet, mahogany-colored onions. That concentrated sweetness is the soul of the soup. Everything else — the beef broth, the cognac, the cheese — builds on that foundation.
Ingredients
- 1.4 kg (3 lbs) yellow onions (about 5 large), thinly sliced
- 4 tbsp unsalted butter
- 1 tbsp olive oil
- 1 tsp kosher salt
- ½ tsp sugar (helps caramelization)
- 3 garlic cloves, minced
- 240ml (1 cup) dry white wine or dry vermouth
- 2 tbsp cognac or brandy (optional but recommended)
- 1.5 L (6 cups) high-quality beef broth
- 2 sprigs fresh thyme
- 1 bay leaf
- Salt and pepper to taste
- 4 thick slices crusty baguette or sourdough
- 200g (7 oz) Gruyère cheese, freshly grated
- 50g (2 oz) Parmesan, freshly grated (mix with Gruyère)
Instructions
- Slice onions thinly and evenly. Use a mandoline or a sharp knife. Consistent thickness ensures even caramelization. They'll look like a mountain of onions — this is correct. They'll cook down dramatically.
- Start the caramelization. Melt butter with olive oil in a large Dutch oven over medium heat. Add onions, salt, and sugar. Stir to coat. Cook over medium-low to low heat, stirring every 5–10 minutes. This takes 45–60 minutes. Do not rush it.
- Monitor and adjust. If onions start to stick, add a tablespoon of water and scrape the bottom. You want to build up and dissolve the fond (brown bits) repeatedly — that's where the flavor lives. Finished onions should be dark mahogany, jammy, and sweet.
- Add garlic. Add minced garlic and cook 2 minutes, stirring constantly.
- Deglaze with wine. Pour in the white wine, scraping up all the browned bits from the bottom of the pot. Add cognac if using. Cook until the wine evaporates, about 5 minutes.
- Add broth and herbs. Add beef broth, thyme, and bay leaf. Bring to a boil, then reduce to a simmer. Cook 20–25 minutes. Remove thyme and bay leaf. Taste and adjust salt and pepper.
- Toast the croutons. Brush bread slices with olive oil and toast in a 200°C (400°F) oven for 8–10 minutes until golden and hard. Set aside.
- Assemble and broil. Preheat broiler to high. Ladle soup into oven-safe crocks placed on a baking sheet. Float a crouton on top of each bowl. Pile generously with the mixed Gruyère and Parmesan. Broil 3–5 minutes until cheese is bubbling and golden-brown in spots.
- Serve carefully. The bowls will be extremely hot. Serve immediately — the cheese begins to congeal quickly.
Chef's Pro Tips
- Never cover the onions while caramelizing — the moisture needs to escape for them to brown rather than steam.
- Use a wide, heavy-bottomed pot. More surface area = faster, more even caramelization.
- The soup improves dramatically the next day. Make it 24 hours ahead and reheat gently.
- Real Gruyère (from Switzerland) melts better than the domestic versions. Look for it at Trader Joe's or any good cheese counter.