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Low-Carb French Onion Soup

5 stars, average of 7 ratings

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French onion soup is a beloved comfort food classic, and this rich, caramelized onion soup version takes it to the next level. Served over chunks of bread topped with melted cheddar, it's traditionally a carb-heavy dish. Our version, however, is a delightful low-carb alternative that still captures that indulgent comfort food essence.

For the cheesy toasts, I've opted for Sourdough Keto Baguettes recipe to keep it keto and gluten-free, but feel free to use any keto bread you prefer. The cheese is melted onto the toasts before adding them to the soup, ensuring they stay crisp and don’t get soggy too quickly.

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Hands-on Overall

Serving size about 1 1/3 cups/ 320 ml, with 2 slices of cheesy toast

Allergy information for Low-Carb French Onion Soup

✔  Gluten free
✔  Egg free
✔  Pork free
✔  Avocado free
✔  Coconut free
✔  Fish free
✔  Shellfish free

Nutritional values (per serving, about 1 1/3 cups/ 320 ml, with 2 slices of cheesy toast)

Net carbs8.8 grams
Protein17.1 grams
Fat26.8 grams
Calories373 kcal
Calories from carbs 10%, protein 20%, fat 70%
Total carbs16.6 gramsFiber7.9 gramsSugars7.1 gramsSaturated fat11 gramsSodium1,114 mg(48% RDA)Magnesium166 mg(42% RDA)Potassium664 mg(33% EMR)

Ingredients (makes 6 servings)

Cheesy Keto Toasts:
  • 4 tbsp unsalted butter or ghee (60 ml)
  • 3 large brown onions, sliced (450 g/ 1 lb)
  • 1 bay leaf
  • 1/2 cup dry white wine (120 ml/ 4 fl oz)
  • 4 cups beef stock (960 ml/ 32 fl oz)
  • 3 cups water (700 ml/ 24 fl oz)
  • thin strips of peel from 1/2 organic lemon
  • 1 tbsp Dijon mustard (15 ml)
  • 1 tsp salt, or to taste
  • black pepper, to taste


  1. Preheat oven to 200 °C/ 400 °F (conventional), or 180 °C/ 355 °F (fan assisted). To make the toast, follow directions here but instead make one large baguette. Allow baguette to cool completely while you make the soup.
    Note: You will only be using one large baguette, and need only half of the mixture, so you can either use half of the ingredients to make one large baguette, or make the whole recipe and use the remainder to eat as per usual. Low-Carb French Onion Soup
  2. Heat the butter in a large saucepan over low-to-medium heat. Thinly slice the onions and add to the pan. Reduce heat to low and cook, stirring every few minutes, for 30 mins or until onions have softened and starting to brown.
    Low-Carb French Onion Soup
  3. Increase heat to medium high, add 1 tsp salt and cook, stirring frequently, around 10 minutes until caramalized.
    Low-Carb French Onion Soup
  4. Reduce the heat slightly, add the wine and simmer, stirring, until the wine is nearly evaporated, around 2 minutes. Add the bay leaf, lemon peel and season with 1 tsp salt.
  5. Add the stock, water, and reduce heat to low, cover and simmer gently for 20 mins or until flavors develop. Whisk in mustard. Add salt and pepper to taste.
  6. To make the cheesy toast, slice the baguette into about 1/2 inch (1 1/4 cm) slices. Layer on a baking tray and place under a grill/broiler. Cook until golden brown and then remove.
    Low-Carb French Onion Soup
  7. Flip over, top with grated cheese, and return to the broiler.
    Low-Carb French Onion Soup
  8. Serve with cheesy toast and soup. Serve immediately while still hot. To store the soup (without the toast), let it cool down and keep in the fridge for up to 5 days, or freeze for up to 3 months. The toast should always be make fresh. Low-Carb French Onion Soup

Ingredient nutritional breakdown (per serving, about 1 1/3 cups/ 320 ml, with 2 slices of cheesy toast)

Net carbsProteinFatCalories
Sourdough Keto Baguettes (KetoDiet blog)
2.9 g8.1 g10.9 g155 kcal
Cheese, Swiss , Gruyère
0.1 g5.7 g6 g78 kcal
Butter, unsalted, grass-fed
0 g0.1 g7.7 g68 kcal
Onion, brown (yellow), raw
4.8 g0.7 g0.1 g27 kcal
Bay leaf, dried
0 g0 g0 g0 kcal
Wine, white, dry
0.4 g0 g0 g16 kcal
Beef bone broth, beef stock
0.3 g2.4 g2 g27 kcal
Water, still
0 g0 g0 g0 kcal
Lemon zest (peel), fresh
0 g0 g0 g0 kcal
Dijon mustard
0 g0.1 g0.1 g2 kcal
Salt, sea salt
0 g0 g0 g0 kcal
Pepper, black, spices
0.1 g0 g0 g0 kcal
Total per serving, about 1 1/3 cups/ 320 ml, with 2 slices of cheesy toast
8.8 g17.1 g26.8 g373 kcal

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Dearna Bond
Creator of

Dearna Bond

Dearna is a passionate foodie and food photographer, and loves sharing her knowledge and enthusiasm for both via her food blog and online photography courses.

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Comments (4)

This soup is exquisite! I went all the way and made the sourdough bread to go with it. So worth it! It's a keeper!

Thank you so much, I'm glad you like it! The bread is a must 😊

WOW this is the BEST onion soup I've had in years! Even my husband loved it and trust me, that's huge compliment 😊 I didn't use the sourdough bread recipe but made your 90 second keto bread instead. So yummy!!

Thank you Lola, the 90 Second Keto Bread is a great swap if you're busy!