If you love low carb French onion soup but don’t want to stand over the stove for hours, this crock pot version is going to be a favorite. It’s rich, deeply flavorful, and gives restaurant-quality French onion soup a run for its money — all while keeping things low carb.
Using the crock pot allows the onions to slowly caramelize and develop that signature depth of flavor, while finishing the soup under the broiler gives you that classic cheesy, bubbly topping everyone loves.
This soup pairs perfectly with something crunchy on the side, like my Low Carb Crackers, which are great for scooping up the cheesy onion broth.
Why You’ll Love This Recipe
- Naturally low carb and keto-friendly
- Made almost entirely in the slow cooker
- Deep, caramelized onion flavor without standing over the stove
- Perfect for cozy dinners, holidays, or meal prep
- Easily customizable with different cheeses
Ingredients
- 3 large onions
- 3 garlic cloves, minced (or 1½ teaspoons minced garlic)
- 6 cups beef broth (or 6 cups of water + 6 tsp of my Keto Beef Bouillon Paste)
- 4 tablespoons butter
- 1 tablespoon Worcestershire sauce
- ½ teaspoon dried thyme
- Salt and pepper, to taste
- Slow cooker
For Topping
- Parmesan crisps (important — see notes below)
- White cheese of choice: Swiss, provolone, or Muenster
Instructions
- Peel and petal the onions by cutting each onion in half, then into quarters. You can cut them into eighths if you prefer, but I like mine left in quarters for a heartier texture.
- Add the onions, minced garlic, butter, Worcestershire sauce, thyme, salt, and pepper to the crock pot.
- Important: Either melt the butter before adding it, or plan to stir the soup about one hour into cooking. This helps distribute the butter evenly and prevents it from sitting on top.
- Cook on LOW for 7 hours, allowing the onions to soften and develop deep flavor.
- After 7 hours, pour in the beef broth and stir well. Continue cooking for 1 additional hour.
Broiling the Cheese
Preheat your broiler.
Ladle the soup into oven-safe ramekins or bowls. Place a Parmesan crisp directly on top of the soup, then add your shredded white cheese.
Why this matters: If you skip the Parmesan crisp (or another barrier like low-carb croutons), the cheese will sink into the soup instead of forming that classic cheesy crust. I’ve tested it — trust me on this step.
Broil for just a few minutes, watching very closely, until the cheese is melted, bubbly, and lightly golden. Broilers work fast!
- Serving Size: 1 cup
- Servings Per Recipe: 8
(Cheese + parmesan crisps not included)
📖 Nutrition Information
Serving Size: 1 cup
Servings Per Recipe: 8
Nutrient Amount Calories 90 Fat 6 g Protein 2 g Total Carbs 7 g Fiber 1 g Net Carbs 6 g Disclaimer: Nutrition information is an estimate only and may vary based on brands used, portion sizes, and substitutions.
Tips & Notes
- Swiss is the classic choice, but Muenster melts a little better.
- Parmesan crisps can be homemade or store-bought.
- If your onions aren’t as caramelized as you’d like, you can cook the first stage slightly longer.
- This soup reheats well and tastes even better the next day.
- For a more filling dinner, serve this low carb French onion soup alongside my Keto Meatloaf for a cozy, comfort-food meal.
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Final Thoughts
This crock pot French onion soup is rich, comforting, and shockingly close to what you’d order at a restaurant — minus the carbs. It’s proof that low-carb cooking doesn’t mean sacrificing flavor.
This low carb French onion soup also works beautifully as part of a cozy dinner spread, especially when paired with my Easy Keto Crock Pot Dinner for a warm, satisfying meal.