French Onion Lentil Soup offers all there is to love about the classic – caramelized onions, a savory broth, and cheesy baguette slices – with the addition of hearty lentils. Warming, nourishing, and sure to become a favorite!

Why You’ll Love this French Onion Lentil Soup

French Onion Soup is a cozy season staple for me.

Between the velvety caramelized onions, rich, savory beef broth, and Gruyere-blanketed bread topping, it’s the true definition of a hug-in-a-bowl.

As incredible as the classic is, I wanted a heartier version of this comforting soup that could serve as a full meal, rather than a starter or side.

Enter: lentils! The humble, endlessly versatile pantry staple that’s both budget friendly and super nutritious. (They also SHINE in my favorite Lentil Soup Recipe.)

Lentils bulk up the soup with protein and fiber, making it much more filling. You can even make the soup completely vegetarian by swapping the beef broth for vegetable broth.

(And if you have any leftover, try my reader-favorite Roasted Veggie Lentil Salad next!)

The Ingredients

• Onions: Slowly caramelized onions are what give French onion soup its depth and body. I prefer using yellow onions, which should be peeled and thinly sliced.
• Butter: The tastiest (French) way to caramelize onions. Although feel free to use vegan butter (or just extra olive oil) to make the soup dairy-free.
• Garlic: Add as little (or as much!) fresh garlic as you wish. I suggest around 4 cloves.
• Herbs: Fresh thyme and a bay leaf add an aromatic, herbal backbone to the broth.
• Tamari: For an instant umami boost! I usually use a lower-sodium version for better salt control.
• Broth: Beef broth richly flavors the cooking liquid for the onions and herbs to simmer in.
• Lentils: For the best results, look for French lentils, also known as Le Puy lentils, or small black (Beluga) lentils.
• Vinegar: A splash of sherry vinegar brightens the broth at the end of cooking. (This takes the place of wine, which is a common ingredient in French onion soup.)
• Bread: For the cheesy toasts on top, I recommend using a crusty baguette. Slice into 12 slices, and reserve any extra for sopping up extra broth.
• Cheese: Gruyere is the classic French onion soup topping, however you can swap it for Asagio, Swiss, Gouda, or Mozzarella, if you prefer.

For a complete list of recipe ingredients and quantities, see the recipe card below.

The Directions

Step 1: Caramelize the Onions.

Start by melting butter and olive oil in a large Dutch oven or stock pot over medium heat. Add onions and cook, stirring every 5 minutes or so, until the onions begin to caramelize. Lower the heat if the onions brown too quickly (I usually do this after about 20 minutes). The caramelization process should take about 40 minutes.

Step 2: Add Aromatics.

Stir in garlic, bay leaf, thyme, and tamari. Cook another 2 minutes.

Step 3: Add Lentils and Broth.

Bring soup to a boil, reduce heat, and simmer with the lid slightly ajar for about 40 minutes, until the lentils are tender.

Step 4: Remove Thyme and Bay Leaf, and give the soup a taste. Season as needed with extra salt and pepper.

Step 5: Ladle Soup into Bowls (make sure they’re oven-safe), top with the bread and cheese, and broil for 3 to 5 minutes, until golden and melty.

Recipe Variations

• Skip the Broiling Step. If you don’t have oven-safe bowls, don’t fret! Simply arrange your baguette slices on a baking sheet and top them with grated cheese, and broil until the cheese is melty. Ladle your soup into bowls, and top with cheesy toasted bread.
• Use Dried Herbs. If you don’t have fresh thyme on hand, 1 teaspoon of dried thyme or herbs de Provence will also work.
• Make Vegetarian. Swap the beef broth for vegetable broth. You can also make this soup vegan by using vegan butter (or extra olive oil), and your favorite brand of plant-based cheesy shreds.
• Make Gluten Free. This recipe does not include flour like some traditional French onion soup recipes do. However you will need to use a gluten free baguette for the bread topping.

Serving Suggestions

While this French onion lentil soup is hearty enough to make a full meal, it pairs beautifully with a salad or roasted veggies. Here are a few suggestions:

• Cauliflower. I especially love this Roasted Cauliflower with Fried Caper Gremolata. My Moroccan Cauliflower recipe is also a reader favorite (and only 5 ingredients!).
• Brussels Sprouts. Try my Crispy Brussels Sprouts with Maple-Mustard Glaze for a stand-out side dish. This Brussels Salad with pears and pecans is always a winner, too!
• Green Salad. This stunning Arugula and Persimmon Salad is perfect for the fall and winter months. You also can’t go wrong with my Arugula Goat Cheese Salad.

How to Store and Reheat

• To Store. Store leftover French onion lentil soup in the fridge for up to 4 days. For best results, store the soup without cheese or baguette topping, and prepare the topping fresh while reheating.
• To Reheat. Warm the soup over the stovetop or in the microwave until steaming. Top with baguette slices and cheese, and pop under the broiler as instructed.

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If you give this recipe a try, I’d love for you to leave a rating and review. Also, be sure snap a pic and tag #dishingouthealth so I can see your beautiful creations.