Classic French Onion Soup with Gruyere Crust
Slow-caramelized onions built into a deep, savory broth enriched with beef stock, cognac, and white wine, then finished with crusty French bread and melted Gruyere cheese under the broiler. A traditional bistro favorite requiring patience for the onions to achieve their rich, mahogany color.
Ingredients
- ¼ cup butter
- 1 tablespoon rendered bacon fatcanola oilequalvegetarian
2
- 8 large onions, thinly sliced into half-moons, approximately 3 lbs
- ½ teaspoon kosher salt
- ½ teaspoon brown sugar
- 1 tablespoon flour
- 8 cups low sodium beef broth, hot
- 1 sprig fresh thyme
- ¼ cup cognac
- 1 cup dry white wine
- 6 thick slices French bread, cut to size of serving bowls and toasted
- 1 ½ cups coarsely grated Gruyere
Instructions
- 1
Heat butter and bacon fat in a heavy saucepan over medium-low heat.
- 2
Stir in onions, cover, and cook slowly, stirring occasionally, until tender and translucent, about 12 minutes.
- 3
Add salt and sugar, increase heat to medium, and continue cooking while stirring frequently to prevent burning until onions are brown, 25 to 30 minutes.
- 4
Sprinkle flour over onions and cook slowly, stirring constantly, for 3 to 4 minutes.
- 5
Remove from heat and whisk in 2 cups of hot stock.
- 6
Return to heat, bring to a simmer, then add remaining stock, thyme, cognac, and wine.
- 7
Cover and simmer over low heat for 1 hour 30 minutes.
- 8
Remove thyme sprig and simmer for another 15 minutes, adding water if liquid reduces too much. Taste and adjust seasoning.
- 9
Divide soup among 6 ovenproof bowls.
- 10
Top each bowl with a slice of toasted French bread and sprinkle 1/4 cup grated cheese over each.
- 11
Place bowls on a baking sheet and broil under preheated broiler until cheese melts and forms a crust.
- 12
Serve immediately.
Tips
Patience is essential during caramelization; resist the urge to increase heat significantly as this risks burning rather than browning the onions.
Use a heavy-bottomed pan to ensure even heat distribution and prevent scorching.
For deeper flavor, use Comte cheese as suggested in the source instead of standard Gruyere.
Good to Know
Refrigerate covered up to 3 days. Freeze soup (without bread and cheese topping) up to 2 months.
Prepare soup completely through step 8. Refrigerate up to 1 day. Reheat gently before adding bread and cheese for broiling.
In warmed ovenproof bowls immediately after broiling while cheese is hot and crispy.
Common Mistakes
Do not rush the onion caramelization by raising heat too high to avoid burnt, bitter onions instead of sweet, caramelized ones.
Do not skip whisking in stock away from heat to avoid flour lumps forming in the hot broth.
Do not leave unattended under the broiler to avoid burning the cheese and bread.