# French Onion Soup with Cheese

> All the flavour of French onion soup comes from **the slow caramelisation** that takes **45 minutes over low heat**. Any shortcut gives you ordinary onion soup — the onion must turn deep brown and sweeten before the liquid goes in.

**French Cuisine · 80 min · 5 servings · 340 kcal per serving**

Onion soup is one of the cheapest and best-known French soups, and almost all of it is onion. Which is why there is no room for shortcuts — time is the main ingredient.

## Ingredients

- 6 — large onions, sliced
- 4 tbsp — butter
- 1 tbsp — olive oil
- 1 tsp — sugar
- 1 tbsp — flour
- 6 cups — beef stock
- 2 — bay leaves
- 1 tsp — dried thyme
- 1 tbsp — balsamic vinegar
- 8 slices — baguette
- 2 cups — Gruyère or mozzarella

## Method

1. **Slice the onion** — Cut the onion into **thin, even slices** of the same thickness. Uneven slices caramelise at different rates, so some burn while others stay raw.
2. **Start the caramelisation** — Melt the butter with the oil and add the onion, salt and sugar over **medium heat for 10 minutes**, stirring. The onion will release water first — let it evaporate.
3. **Slow caramelisation** — Lower the heat and continue for **35 minutes**, stirring every 5 minutes. The onion must reach a **deep brown** rather than golden — that is the entire source of flavour.
4. **Deglaze** — When the base browns, add a little stock and **scrape the base with a wooden spoon**. That brown layer is called fond and is packed with concentrated flavour.
5. **Flour and liquid** — Sprinkle in the flour and stir for two minutes, then pour in the stock with the bay and thyme and simmer for **20 minutes**. Add the vinegar at the end.
6. **Toast and cheese** — Toast the bread slices, ladle the soup into ovenproof bowls, and set the bread and cheese on top. Under the **grill for 4 minutes** until the cheese melts and browns.

## Tips

- 45 minutes of caramelisation is not optional — any shortcut gives ordinary onion soup.
- Evenly thick slices, or some burn while others stay raw.
- Scrape the browned base — it is the richest part of the flavour.
- A spoonful of vinegar at the end lifts the whole dish and balances the onion's sweetness.

## FAQ

### Why does my onion soup taste ordinary?
The onion was not caramelised enough. It needs 45 minutes over low heat to reach a deep brown. Pale gold means you are only halfway — the sweetness and depth arrive in the last 15 minutes.

### Can I speed up the caramelisation?
A little: a spoonful of sugar and a small pinch of bicarbonate speed the reaction by 10-15 minutes. But there is no real shortcut — the onion needs time for its sugars to caramelise.

### What replaces Gruyère?
Mozzarella with a little parmesan gives a close result: the mozzarella melts and the parmesan brings the sharpness. Gruyère does both, but this substitute works well.

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Source: https://hanakoleah.com/en/french-cuisine/french-onion-soup-with-cheese
Edited by: Marwa Mohamed
Last updated: 2026-10-29