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My keto French onion soup recipe features caramelized onions swimming in warm broth with crusty bread and melty cheese. It’s made with no flour, no thickeners, and only 3 grams of net carbs!
Ready for more low-carb soup recipes? Try my keto taco soup, keto chicken soup, and keto broccoli cheese soup next.
Surprisingly, there are few low-carb French onion soup recipes.
I suppose it makes sense, considering the main ingredients in French onion soup are decidedly not keto-friendly (note: bread, wine, and onions). Luckily, with a few low-carb substitutions, it can become a staple of any keto diet.
Table of Contents
Why I love this recipe
- Simple ingredients. There are no complicated or over-the-top substitutions needed.
- Comfort food at its finest. We’re talking savory broth, sweet onions, toasted bread, and layer upon layer of melted cheese.
- Surprisingly easy to make. For how fancy this looks, I swear it’s one of the easiest soups you’ll ever make.
- Ready in 20 minutes. And a bulk of that time is spent letting the onions and soup simmer on the stovetop.
Ingredients needed
- Butter. I suggest using unsalted butter since we’re using salty ingredients.
- Onions. White onion is preferred, but yellow onions or sweet onions can also work, just not red onions. Slice them finely so they cook quickly.
- Granulated sweetener. Just a pinch to balance out the salty flavors. I use allulose, as it dissolves exactly like sugar does.
- Salt and black pepper. To taste.
- Beef broth. Essential for French onion soup. I prefer using premade broth instead of bouillon cubes.
- Worcestershire sauce. Adds a lovely complex flavor and enhances the meaty flavors.
For the toasted cheesy bread:
- Keto buns. Traditional French onion soups typically use sliced baguette. To replicate this, we’ve used thinly sliced keto hot dog buns. You can also use thickly sliced keto bread or even keto rolls.
- Gruyere cheese. Another must for French onion soup! Always use freshly grated cheese, which has a better flavor and melts smoothly.
- Fresh thyme. To serve.
How to make keto French onion soup
I’ve included step-by-step photos below to make this recipe easy to follow at home. For the full printable recipe instructions and ingredient quantities, scroll to the recipe card at the bottom of this post.
Step 1- Prep. Preheat the oven to 200C/400F and line a large baking sheet with parchment paper.
Step 2- Sauté onions. Place a large soup pot over medium heat. Once hot, melt the butter. Add the sliced onions, sweetener, salt, pepper, and sauté for 8-10 minutes.
Step 3- Build the broth. Add the beef broth and Worcestershire sauce and bring to a simmer. Once simmering, cover the pot and let it simmer for 10 minutes.
Step 4- Prepare the cheesy bread. Slice the keto bread into six thick slices, then slice each in half. Place the twelve pieces of bread onto the prepared baking sheet. Sprinkle the cheese on top. Bake the bread for 6-8 minutes or until golden brown.
Step 5- Assemble. Ladle soup into small bowls. Add 1-2 pieces of the cheesy toast on top and sprinkle with extra cheese and thyme sprigs.
Arman’s recipe tips
- Can’t find gruyere? Use mozzarella, white cheddar, or Swiss cheese instead.
- Don’t cut the onions too thin. Otherwise, you risk them cooking too quickly and shriveling up by the time the soup is cooked. I usually stick to ¼-inch in thickness.
- Sauté garlic. For additional aromatics.
- Broil. When time allows, I like to ladle the soup into oven-safe bowls and then place them in the oven on the broiler setting for 30 seconds. This crisps up the bread and helps the cheese get even more melty.
Storage instructions
To store: Leftover soup can be stored in an airtight container in the refrigerator for up to one week.
To freeze: Place the cooled soup in an airtight container and store it in the freezer for up to six months.
Reheating: Microwave soup in 30-second intervals or reheat in a saucepan until warm.
To make-ahead: Prepare the soup up to three days in advance and store it in the fridge. Before serving, warm it on the stove over medium low heat, then serve with the cheesy croutons.
Frequently asked questions
The main difference between onion soup and classic French onion soup is that the latter uses beef stock or beef broth. A generic onion soup often uses vegetable broth or sometimes chicken broth.
Yes, to make vegetarian French onion soup, use vegetable broth and a vegan-friendly Worcestershire sauce.
More keto comfort food dishes you’ll enjoy
Keto French Onion Soup
Ingredients
- 1 ounce butter
- 4 large onions thinly sliced
- 1/2 teaspoon allulose or any granulated sweetener
- 1/2 teaspoon pepper
- 32 ounces beef broth
- 3 tablespoons Worcestershire sauce
For the cheesy toasts
- 2 keto hot dog buns * See notes
- 1 1/2 cups Gruyere cheese finely shredded
- 4 springs Thyme loosely torn
Instructions
- Preheat the oven to 200C/400F. Line a large baking sheet with parchment paper and set aside.
- Place a large soup pot over medium heat. Once hot, add the butter to melt. Add the sliced onions, sweetener, and pepper and saute for 8-10 minutes, until tender.
- Add the beef broth and Worcestershire sauce and bring to a simmer. Once it starts simmering, cover the pot and let it simmer for a further 10 minutes.
- While the soup is simmering, prepare the cheesy toasts. Slice your two keto hot dog buns into 6 thick slices and slice each one in half. Place the twelve pieces of bread onto the lined sheet. Sprinkle half the Gruyere cheese over the top. Bake in the oven for 6-8 minutes, until golden brown.
- Ladle the soup into small bowls. Add 1-2 pieces of the cheesy toast on top of each soup bowl and sprinkle with extra Gruyere cheese and a sprig of thyme.
Because no one is ever perfect, I give four stars for your onion soup. French onion soup has always been a favorite of mine, even since I was a young teen. Then I decided to go keto and I had no idea how to or what to cook. I sure thank you for your quick and easy recipes. Way to go and the biggest thing I have to say thank you for? Your recipes are free! Not trying to make a big buck on us internet folk! Now that’s the best news I’ve heard all day.