Here’s a classic French Onion Soup (Soupe à l’Oignon) recipe with detailed, step-by-step instructions for perfectly slow-cooked onions and a rich, restaurant-style finish.

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🧅 Classic French Onion Soup (Serves 4–6)

🛒 Ingredients

For the slow-cooked onions:

• 4 large yellow onions (about 2½–3 lbs / 1.2 kg), thinly sliced

• 3 tbsp unsalted butter

• 1 tbsp olive oil

• 1 tsp salt (adjust to taste)

• 1 tsp sugar (optional, helps caramelization)

• 2 cloves garlic, minced

For the soup base:

• 1 tbsp all-purpose flour

• ½ cup dry white wine (or dry sherry)

• 6 cups good quality beef stock (traditional) or beef + chicken mix

• 1 bay leaf

• 2–3 sprigs fresh thyme (or ½ tsp dried)

• Freshly ground black pepper

For the topping:

• 1 baguette, sliced into 1-inch rounds

• 1½–2 cups grated Gruyère cheese

• Optional: mix of Gruyère + Swiss or mozzarella

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🔥 Step-by-Step Instructions

Step 1: Prepare the Onions Properly

1. Peel onions.

2. Cut in half from root to stem.

3. Slice thinly into even half-moons (about ⅛ inch thick).
   ➜ Uniform slices ensure even caramelization.

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Step 2: Start the Slow Caramelization (Most Important Step)

1. In a heavy-bottomed Dutch oven or large pot, heat:

   • 3 tbsp butter

   • 1 tbsp olive oil
     over medium heat.

2. Add sliced onions and salt. Stir well.

3. Cook uncovered for 10 minutes, stirring occasionally.
   The onions will soften and release moisture.

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Step 3: Slow Cook Until Deep Golden Brown

Reduce heat to medium-low.

Cook for 35–50 minutes, stirring every 5 minutes.

What to expect:

• 15 min: Soft and translucent

• 25 min: Light golden

• 35–45 min: Deep golden brown

• 45+ min: Rich brown with sweet aroma

If onions start sticking:

• Add 1–2 tbsp water and scrape bottom (this adds flavor).

Optional: Add 1 tsp sugar if onions aren’t browning well.

👉 Do not rush this step. Proper caramelization creates the signature deep flavor.

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Step 4: Add Garlic & Flour

1. Stir in minced garlic. Cook 1 minute.

2. Sprinkle 1 tbsp flour over onions.

3. Stir continuously for 2 minutes.

This thickens the soup slightly and adds body.

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Step 5: Deglaze with Wine

1. Pour in ½ cup white wine.

2. Scrape bottom of pot to release browned bits.

3. Simmer until wine reduces by half (about 3 minutes).

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Step 6: Add Stock & Herbs

1. Pour in 6 cups hot beef stock.

2. Add:

   • Bay leaf

   • Thyme

   • Black pepper

3. Bring to gentle simmer.

4. Cover partially and cook 20–30 minutes.

Taste and adjust salt.

Remove bay leaf and thyme stems before serving.

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🥖 Step 7: Prepare the Bread

1. Preheat oven to 375°F (190°C).

2. Arrange baguette slices on tray.

3. Toast 8–10 minutes until dry and crisp (both sides lightly golden).

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🧀 Step 8: Broil with Cheese (Classic Finish)

1. Ladle hot soup into oven-safe bowls.

2. Place toasted baguette slices on top.

3. Cover generously with grated Gruyère.

4. Place bowls on baking sheet.

5. Broil 2–5 minutes until cheese bubbles and browns.

⚠ Watch carefully — it browns fast!

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🍽 Serve Immediately

The top should be:

• Crispy edges

• Gooey melted cheese

• Deep brown onion broth underneath

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🧠 Pro Tips for Restaurant-Quality Flavor

• Use homemade beef stock if possible.

• Cook onions low and slow — this is 70% of the flavor.

• A splash of brandy before the wine adds depth.

• For extra richness, finish with a tiny knob of butter stirred in before serving.