Smoky French Onion Soup Recipe

Traditional recipes for French Onion Soup call for beef stock but this vegetarian version uses Halen Môn's smoky Dijon mustard and dry sherry for an extra savoury dimension. It’s made more umami with the addition of black garlic ketchup too, but this is optional.

The soup can be made up to three days in advance and stored in a sealed container in the fridge until ready to reheat and serve.

Recipe created by Halen Mon.

Ingredients for the soup Serves: 4

Ingredients for the croutons

  • 8 slices of baguette, cut at a slight angle
  • 1 garlic clove
  • 8 tsp smoky Dijon mustard
  • 150g Gruyère cheese, grated


  1. Heat the butter and oil in a large saucepan until the butter starts to sizzle. Add the onions and salt and cook over a medium heat with the lid on, removing the lid to stir occasionally for about 10 minutes. By this point the onions should have slumped and turned translucent. Remove the lid and turn the heat down. Continue to cook, stirring regularly for 10 minutes more, until the onions begin to take on golden edges. Sprinkle over the sugar, and a good grind of black pepper, and stir through the onions. Cook for another 25 minutes or so until deeply caramelised. Taste a slice of onion – it should taste sweet and jammy.
  2. Stir in the herbs, wine and Dijon mustard and stir to combine. Cook until all of the wine has been absorbed, about 2-3 minutes. Add the stock, soy sauce and Black Garlic Ketchup (if using) and stir to combine. Taste the soup and add more salt and/or pepper if you prefer. Bring to a simmer, then cook at a gentle simmer, uncovered for 20 minutes until thickened slightly (remember the croutons will absorb a lot of liquid from the soup in the bowls).
  3. When ready to serve, lightly toast the baguette slices in a toaster or under the grill and rub each slice with the garlic clove. If your soup bowls aren’t oven-proof, arrange the slices on a baking sheet and divide the smoky Dijon mustard between the slices. Top with the grated cheese and place under the grill until melted and bubbling. Divide the sherry between the bowls, top with the onion soup and a couple of cheesy croutons each.
  4. If you prefer to use oven proof bowls (and for a more cheesy soup), divide the sherry between oven-proof bowls or ramekins, spoon ¼ of the soup into each bowl and top with 2 slices of baguette. Spoon a teaspoon of the smoky Dijon mustard onto each slice and top with the grated Gruyère. Place under a hot grill until the cheese is melted and bubbling. Serve straight away, but be mindful that it will be piping hot.
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