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Batch 021

French onion
soup.

Dinner Grass-fed beef broth
1 hour 15 minutes Serves 4 Grass-fed beef bone broth

The dish where the quality of your broth matters most. Ours has had eighteen hours of head-start, so the rest is mostly patience: slowly caramelised onions, a good wine, aged Gruyère.

Ingredients
  • 1L Grass-Fed Beef Bone Broth
  • 1kg white or yellow onions (about 5 large), thinly sliced
  • 4 tbsp butter + 2 tbsp olive oil
  • 2 cloves garlic, crushed
  • 200ml dry white wine or dry sherry
  • 1 tsp fresh thyme leaves
  • 1 tsp sea salt
  • 4 slices sourdough bread
  • 150g Gruyère or aged Comté, grated
Method
  1. Melt butter with olive oil in a large heavy pot over medium-low heat. Add onions and salt. Cook slowly — very slowly — for 40–50 minutes until deeply caramelised and jammy. Don't rush this. The onions should be a deep amber-brown.
  2. Add the garlic and thyme and cook 2 more minutes.
  3. Add the wine and scrape up any caramelised bits from the bottom of the pot. Cook until the wine is mostly absorbed.
  4. Pour in the bone broth. Simmer for 15 minutes. Taste and adjust seasoning.
  5. Ladle into oven-safe bowls. Place a slice of sourdough on top of each bowl. Pile on the grated cheese.
  6. Grill under a hot broiler for 3–5 minutes until the cheese is bubbling and golden.
More recipes

Keep cooking.

Recipe Bone broth risotto 40 min · Serves 2 · Liquid Gold → Recipe Classic Lisbon caldo verde 35 min · Serves 4 · Grass-fed beef → Recipe Turmeric bone broth soup 20 min · Serves 2 · Liquid Gold →
"The onions need an hour, not twenty minutes. That's where the colour comes from, that's where the flavour comes from."
— from the kitchen, on this recipe
Common questions

A few things people ask.

Yes. There is no shortcut. The onions need to lose their water, then their bite, then their colour, in that order. Rushing the heat scorches the sugars and you end up with bitter brown rather than deep amber. Put the radio on; this is a stirring meditation.
You can, but you'll lose the dish. French onion soup is built on the depth that beef broth provides; chicken makes it taste like onion soup, not French onion. If beef isn't an option, mushroom broth gives you a closer second.
Yes, and it's better for it. The onions and broth keep happily in the fridge for three days, and the flavour rounds out overnight. Reheat, ladle into bowls, top with sourdough and Gruyère, and grill just before serving.
The base freezes well for up to three months. Don't freeze the bread or cheese top; assemble those fresh after thawing. Defrost overnight in the fridge and warm slowly on the stove.
Either, honestly. Aged Gruyère is the traditional choice, slightly nuttier and more assertive. Comté is a touch sweeter and melts beautifully. Avoid pre-grated supermarket cheese; the anti-caking starch makes for a gluey crust rather than a bubbling one.
You can. Skip the wine and add an extra splash of broth with a teaspoon of sherry vinegar at the same stage. You lose some complexity, but the caramelised onions are doing most of the work anyway.

Cooked, tested and written by Sinead McInerney in our Lisbon kitchen. Last reviewed: April 2026.