Ingredients
- 2 tbsp extra virgin olive oil
- 1 kg onions (a mix of brown and red), thinly sliced
- ½ tsp sea salt
- 2 garlic cloves, crushed
- A few sprigs of thyme and 1 bay leaf
- 1 tbsp wholemeal spelt flour (or buckwheat flour for gluten-free)
- 1.2 litres beef or chicken bone broth (see our Healing Bone Broth)
- 1 tbsp balsamic vinegar or apple cider vinegar
- 1 tsp tamari
For the croutons
- 4 slices of sourdough, or our Golden Linseed Loaf for gluten-free
- 80 g Gruyère or Comté, grated
Method
- Caramelise the onions: heat the oil in a large, heavy pan. Add the onions and salt, stir well, then cook over a low heat for 45–50 minutes, stirring every few minutes, until they are deep golden brown, soft and sweet. Don't rush this: slow caramelising is the secret of the soup.
- Add the flavourings: add the garlic, thyme and bay and cook for 2 minutes. Sprinkle over the flour and stir for 1 minute.
- Simmer: add the vinegar and stir to lift the brown bits from the bottom of the pan, then gradually stir in the broth and tamari. Simmer for 20 minutes. Season and remove the herb stalks.
- Make the croutons: heat the grill. Toast the bread on one side, turn it over, cover with cheese and grill until bubbling.
- Serve: ladle the soup into warm bowls and float a cheese crouton on top of each.
Why it's good for you: Onions are one of the richest sources of quercetin, a protective plant compound, and of inulin, a prebiotic fibre that feeds friendly gut bacteria. Making the soup with a long-simmered bone broth adds gelatin and minerals, turning a bistro favourite into a deeply nourishing meal.
Good to know: The traditional recipe uses wine and sometimes brandy; this version uses a splash of vinegar instead, for depth without the alcohol. For gluten-free, use buckwheat flour and the linseed loaf.
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