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Belgian Onion Soup

This Belgian onion soup is a sophisticated, vegetarian twist on the traditional French classic. By using Trappist ale, specifically Chimay Blue, the broth develops a remarkable depth of flavour that balances the natural sweetness of the slowly caramelised onions and shallots. The result is a dark, savoury and incredibly fragrant soup that feels both indulgent and deeply comforting, perfect for chilly autumn evenings or a slow-paced weekend lunch.

For the best results, serve this hearty dish in individual oven-proof bowls topped with thick slices of toasted sourdough and plenty of nutty Gruyère cheese. Grilling the bread and cheese directly on top of the soup creates a bubbling, golden crust that is essential for the authentic experience. While delicious when made fresh, the flavours mature beautifully if left in the fridge overnight and reheated the following day.

Continue reading below

Ingredients for Belgian Onion Soup

  • 2 tablespoons butter

  • 2 tablespoons of extra virgin olive oil

  • 5 large onions, halved and sliced thin

  • 6 cloves of garlic, minced

  • 4 shallots, sliced thin

  • 750 milliliter Chimay Blue

  • 4 cups vegetable stock

  • 4 bay leaves

  • 6 sprigs of thyme

  • 1/2 teaspoons ground white pepper

  • 4 slices sourdough bread for garnish

  • 230g Gruyère cheese for garnish

  • Sea salt to taste

  1. Heat a wide pot or cast-iron on medium heat. Add the butter and let it blister.

  2. Add the onion and cook uncovered. Let them sit for about four minutes and then stir. Repeat until the onions have all begun to brown, at least twenty minutes.

  3. Add the olive oil, garlic, and shallots and stir in the same fashion as before, once every five minutes, until the garlic and shallots have caramelized.

  4. Add 600ml the beer and crank the heat to just shy of high. Let the beer boil off until there is half as much beer volume as onion volume.

  5. Add the stock, bay leaves, thyme leaves, and white pepper. Cook until the liquid has reduced by about two finger widths. Taste the soup and add salt to adjust. Cook for at least an additional twenty minutes before garnishing. In an ideal world, you would let the soup sit a day before serving it. (Just be sure to reheat it.)

  6. Take a slice of sourdough and cut it to fit your bowl or cup. Set atop the soup and cover with several slices of Gruyère. Grill until brown and serve hot, topped with extra thyme.

Disclaimer

While every effort has been made to ensure the information is accurate and up to date, individual needs may vary and dietary requirements can differ based on personal health conditions. Always check food labels and allergen information before preparing or consuming any recipe. If you have specific health concerns, allergies, intolerances, or are following a medically prescribed diet, seek advice from your GP, pharmacist, or a registered dietitian before making significant changes to your diet or lifestyle.

Article history

The information on this page is peer reviewed by qualified clinicians.

  • 28 Jan 2026 | Originally published

    Authored by:

    UK recipe editors

    Peer reviewed by

    UK recipe editors
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