Best French Onion Soup Recipe (Bistro-Style)

French onion soup (soupe à l’oignon) hit iconic status as gratinée des Halles in 19th-century Paris: patiently cooked, jam-like onions, stock, a splash of wine or brandy, and a toast-and-cheese cap broiled to a bubbling crust-popularized by the bistros around Les Halles.

Ingredients

(serves ~6; ranges let you tune intensity)

Fats & aromatics

• Olive oil - 2–3 tbsp (30–45 ml)

• Butter - 80–120 g (6–9 tbsp)

• Yellow/brown onions - 1.1–1.4 kg (5–7 large / 2½–3 lb), thinly sliced

• Optional: 1 small leek (white/light green), 3 small shallots, 4–5 garlic cloves

Seasoning & body

• Fine sea salt, freshly ground black pepper

• Bay leaves - 2–3

• Fresh thyme - 4 sprigs

• Flour - 4–5 tbsp (32–40 g) (classic bistro thickness; GF swap below)

Deglaze & liquid

• Brandy/cognac - 120–150 ml (½–⅔ cup) (house default)

  • or dry white wine / dry vermouth - 150–250 ml (⅔–1 cup)

• Chicken stock - 0.75–1.0 L (3–4 cups) (cleaner onion focus)

  • Beef stock (darker, deeper) or vegetable stock (lighter) also works; water in a pinch

For the gratin

• Sourdough bread, thick slices (see How to Make Homemade Sourdough Bread: A Beginner’s Guide)

• Aged melting cheese, 200–300 g (7–10 oz) - Gruyère AOP is the classic; Comté (PDO) or Emmentaler AOP are excellent alternatives/blends.

Equipment

• Wide heavy pot/Dutch oven (6–8 L / 6–8 qt)

• Wooden spoon

• Ladle

• Oven-safe bowls/crocks

• Sheet tray

• Mandoline (optional)

Helpful reads while you cook:

• The Science Behind the Maillard Reaction: Unlocking the Secret of Browning and Flavor

• Deglazing: Turning Fond into Flavorful Magic

• How to Sauté: A Beginner’s Guide to Perfectly Cooked Ingredients

• How to Make Chicken Stock: A Comprehensive Guide for Flavor and Health

• How to Make the Best Chicken Broth

• How to Make Homemade Sourdough Bread: A Beginner’s Guide

Easy French Onion Soup: Step-by-Step

1. Slice patiently
   Halve onions pole-to-pole; slice thin for even caramelization (a mandoline helps).
   

2. Low & slow caramelization (the soul)
   Warm olive oil on low. Add onions; if the pot looks dry, add butter in small knobs. After 10-20 minutes, add some salt to draw moisture.
   Aim for deep amber, jammy onions - truly like onion jam, not merely soft. Expect 45–70 minutes, depending on pan width and heat.
   

3. Aromatics & flour
   At deep gold, add grated garlic (2-3 min.). Sprinkle in flour; stir 2–3 minutes to cook it (a light roux). Add bay and thyme.
   

4. Deglaze
   Pour in brandy/cognac (or wine/vermouth) and scrape up the fond thoroughly. Reduce by about half or more to mellow alcohol harshness. (Cooking significantly reduces alcohol but may not eliminate it entirely; for zero-alcohol needs, see Variations.)
   

5. Broth & simmer
   Add chicken stock gradually (one dl at a time and stir). Simmer gently 15–25 minutes. Season to taste. Off heat, swirl in 1–2 tbsp butter for sheen if desired.
   

6. Gratin
   Toast sourdough slices. Ladle soup into crocks, float toast, and smother with cheese. Broil until bubbling and well-browned.

Pro Tips

• Width beats depth. A wider pot evaporates faster and browns cleaner.

• Oil → butter ladder. Oil tolerates heat early; butter adds flavor and gloss later.

• Season in layers. Early pinch of salt; final tuning after reduction.

• Cheese matters. AOP/PDO cheeses like Gruyère/Emmentaler ensure traditional making and reliable melting/browning.

Make It Yours (Tuning)

• Thickness: 2–3 tbsp flour = brothy; 4–5 tbsp = bistro “coat-the-spoon” (default).

• Intensity: 0.75 L stock = onion-forward; 1.0 L = lighter.

• Base: Chicken = cleaner onion voice; Beef = darker, steakhouse depth; Veg = light. If needed, water works, but stock gives the backbone.

• Onion mix: 100% yellow/brown = classic; add a little leek/shallot for perfume; garlic optional.

Cheese Quick-Guide (Gruyère vs. Comté vs. Emmentaler)

Gruyère AOP - the bistro benchmark

• Flavor: nutty, gently fruity; deepens with age.

• Melt/browning: superb for gratins; protected under AOP/PDO rules. 
  

Comté (PDO) - complex French depth

• Flavor: buttery-fruity when young; nuttier and more pronounced with longer affinage (≥4 months).

• Melt/browning: excellent; adds richness to the blend.
  

Emmentaler AOP - softer profile, great “stretch”

• Flavor: mild-nutty; classic “eyes” from fermentation during affinage.

• Melt/browning: reliable melt and pleasant pull; made by traditional village dairies.
  

Suggested blends (adjust to taste):

• 70% Gruyère + 30% Comté → classic, nutty-deep profile

• 60% Gruyère + 25% Comté + 15% Emmentaler → extra stretch, rounder sweetness
  

[PHOTO] Cheese trio — insert here

Tip: With a beef + brandy base, bump Comté for gravity. With a chicken/veg base, keep Gruyère-dominant for a brighter onion focus.

Variations

Vegetarian: Robust vegetable stock plus 1 tsp miso or a dash of soy sauce for umami.
Alcohol-free: Deglaze with stock; finish with 1–2 tsp cider vinegar for lift. (USDA/peer-reviewed data: cooking reduces alcohol, but doesn’t always reach 0%.)
Gluten-free: Oat flour 1:1 by weight in place of wheat flour (silky body), or 2 tsp cornstarch slurry stirred in and simmered 3–5 minutes.

Troubleshooting

• Too pale/too sweet: Keep going - time + surface area = deeper browning.

• Bitter edge: Heat was too high; deglaze with a splash of stock, scrape gently, finish with a small knob of butter.

• Too thin: Reduce further, or whisk in 1 tbsp flour (or cornstarch slurry) and simmer 3–5 minutes.

• Cheese won’t brown: Pre-toast bread; move crocks closer to the broiler.

Serving & Pairing

Serve bubbling hot with cracked pepper. Pair with a light red (Gamay/Beaujolais) or a crisp white (Aligoté/Savoy). For the toast, see How to Make Homemade Sourdough Bread: A Beginner’s Guide for a loaf with the ideal structure.

Storage & Reheating

• Fridge: 3–4 days (without bread/cheese).

• Freeze: Up to 3 months; thaw overnight in the fridge.

• Reheat: Gentle simmer; assemble the gratin fresh.

FAQ

Do I need beef stock?

No. Beef is bistro-rich; Chicken Stock or Chicken Broth keeps it lighter (see guides linked above).

Does the alcohol “cook off”?

Cooking greatly reduces alcohol, but retention depends on method/time and may not reach absolute zero. If 0% is important, use the alcohol-free method above. (USDA nutrient-retention data; dietetic literature.)

What’s the best cheese?

Gruyère AOP is the classic; Comté (PDO) and Emmentaler AOP are excellent alternatives/blends for different melt and flavor profiles.

Where did the cheese-topped style come from?

Les Halles-area bistros in 19th-century Paris popularized the gratinéed version.

You Might Also Like These Posts

The Science Behind the Maillard Reaction: Unlocking the Secret of Browning and Flavor
Deglazing: Turning Fond into Flavorful Magic
How to Sauté: A Beginner’s Guide to Perfectly Cooked Ingredients
Chicken Stock
Chicken Broth
How to Make Homemade Sourdough Bread: A Beginner’s Guide