Why You'll Love This French Onion Soup
Gratiné French onion soup is one of the most iconic dishes in French cuisine: slowly caramelized onions, a rich and fragrant beef broth, crispy croutons, and a golden Gruyère topping. A comforting and flavorful dish, worthy of the best Parisian bistros.
Ingredients (serves 4)
- 1 kg yellow onions, thinly sliced
- 60 g butter
- 2 tbsp olive oil
- 1 tsp sugar
- 150 ml dry white wine
- 1.5 litres quality beef broth
- 2 cloves garlic, crushed
- 2 sprigs fresh thyme
- 1 bay leaf
- Salt and pepper to taste
For the gratin
- 8 slices stale baguette, toasted
- 200 g Gruyère (or Comté), grated
Step-by-step preparation
Step 1 – Caramelize the onions
In a large Dutch oven, melt the butter with the olive oil over medium heat. Add the sliced onions and sugar. Cook, stirring regularly, for 40 to 45 minutes until the onions are deeply golden and caramelized. This is the key step — do not rush it.
Step 2 – Deglaze and simmer
Add the garlic and cook for 1 minute. Pour in the white wine and deglaze, scraping up any browned bits. Reduce for 3 minutes. Add the beef broth, thyme, and bay leaf. Season. Simmer over low heat for 20 minutes.
Step 3 – Toast the croutons
Toast the baguette slices in the oven at 180 °C for 8 minutes until golden and crispy. Set aside.
Step 4 – Gratinate and serve
Remove the thyme and bay leaf. Ladle the soup into oven-safe bowls. Place the croutons on top of the soup and generously cover with grated Gruyère. Broil under the oven grill at 220 °C for 3 to 5 minutes until the cheese is golden and bubbling. Serve immediately.
Chef's tips
- Patience: the caramelization of the onions cannot be rushed — this is what gives the soup its full depth of flavor.
- Quality broth: use homemade or high-quality beef broth for optimal results.
- Cheese: aged Comté is an excellent alternative to Gruyère for a more pronounced taste.
- Bowls: it is essential to use oven-safe ceramic bowls for gratinating.
Nutritional information (per serving)
- Calories: ~420 kcal
- Protein: 18 g
- Carbohydrates: 38 g
- Fat: 22 g
FREQUENTLY ASKED QUESTIONS
WHAT IS THE ORIGIN OF FRENCH ONION SOUP?
French onion soup is a French dish whose origins date back to the Middle Ages. It was considered a poor man's dish because onions were cheap. It became a classic of Parisian bistros in the 19th century, especially at Les Halles in Paris where it was served to night workers.
HOW DO YOU CARAMELIZE ONIONS PERFECTLY?
The key is patience and medium heat. Onions should cook slowly for at least 40 to 45 minutes, stirring regularly. They should turn from white to a deep golden color. If browned bits form at the bottom, add a tablespoon of water and scrape them up — this is where the flavor is concentrated.
CAN THE SOUP BE PREPARED IN ADVANCE?
Yes! The soup (without the gratin) can be prepared up to 3 days in advance and stored in the refrigerator. It also freezes very well for up to 3 months. Make the gratin just before serving for perfectly melted and golden cheese.
WHAT CHEESE SHOULD BE USED FOR THE GRATIN?
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