Basic Onion Soup

Six large onions, thinly sliced and cooked slow in olive oil until deeply browned. That’s the whole foundation of a proper French onion soup, and there are no shortcuts. The slow browning caramelizes the natural sugars in the onions, transforming them from sharp and pungent to sweet, jammy, and golden.

Stir constantly during the browning. Onions go from caramelized to burned in seconds, and burned onions taste bitter. Once they’re deeply browned, water and bouillon cubes (or stock if you have it) go in for a quick boil and a 10-minute simmer. That’s enough time for the onion flavor to infuse the broth.

The gratin finish is what makes this soup iconic. Ladle it into oven-proof bowls, float a slice of toasted bread on top, cover completely with grated Gruyere, and broil until the cheese bubbles and browns. The bread soaks up broth from below while the cheese forms a molten cap on top.

Kitchen Tips

• Stir the onions constantly while browning. Low and slow with constant attention is the only way to get even caramelization without scorching.
• Cover the cheese to the edges of the bowl. Any exposed broth will splatter in the oven, and cheese that doesn’t reach the rim won’t form a proper seal.
• Use oven-proof bowls. Regular ceramic can crack under the broiler. Proper French onion soup crocks are worth the investment.

Variations

• Beef broth upgrade: Use rich beef stock instead of water and bouillon for a deeper, more savory base.
• Swiss cheese swap: Gruyere is traditional, but Swiss or provolone melt beautifully and cost less.
• Thyme addition: Add a few sprigs of fresh thyme to the broth during the simmer for a classic herbal note.