Name: French Onion Lentil Soup Recipe
Prep time: 15 min
Cook time: 1 h 5 min
Total time: 1 h 20 min
Cuisine: French
Ingredients: 2 Tbsp. butter; 2 Tbsp. extra-virgin olive oil; 3 large yellow onions (about 2 1/2 to 3 lbs.), peeled and thinly sliced; 4 garlic cloves, minced; 2 tsp. lower sodium tamari; Kosher salt and cracked black pepper to taste; 1 cup petite lentils, such as French (Le Puy) lentils or black (Beluga) lentils; 2 quarts (8 cups) low sodium beef broth (or beef stock); 6 to 8 sprigs fresh thyme (or 1 tsp. dried thyme); 1 bay leaf; 2 Tbsp. sherry vinegar; 8 to 12 (½-inch) slices French bread (from 1 baguette); 1 1/2 cups grated Gruyère cheese

Jump to Recipe· 4.2 from 2 reviews

There’s something truly magical about the rich flavors and hearty textures of this French Onion Lentil Soup Recipe. It’s the kind of dish that feels like a warm hug on a chilly day, combining caramelized onions with tender lentils and a luscious, cheesy crust that elevates every spoonful. If you love comforting meals that are both flavorful and nourishing, this recipe will become one of your go-to favorites in no time.

Ingredients You’ll Need

The image shows two white enamel pots side by side on a white marbled surface. The left pot is filled with thinly sliced raw onions, pale yellow and white in color, layered loosely with smooth, soft textures. The right pot contains cooked caramelized onions, rich brown with a shiny, slightly sticky texture, and a sprig of fresh green thyme on top, the onions appearing soft and slightly wilted. Both pots have a black rim along the edge and white handles. Photo taken with an iphone --ar 4:5 --v 7

Each ingredient in this recipe plays a vital role in building layers of flavor and texture. From the sweetness of caramelized onions to the earthy depth of lentils, and the savory touch of Gruyère cheese, these simple components come together beautifully to make a memorable dish.

2 Tbsp. butter: Adds richness and helps caramelize the onions perfectly for that deep, sweet flavor.
2 Tbsp. extra-virgin olive oil: Balances the butter and brings a subtle fruity note to the base.
3 large yellow onions (about 2 1/2 to 3 lbs.), peeled and thinly sliced: The star ingredient, slow-cooked to golden perfection for natural sweetness.
4 garlic cloves, minced: Infuses a gentle aromatic warmth without overpowering the soup.
2 tsp. lower sodium tamari: Adds umami depth and savory complexity to the onion mixture.
Kosher salt and cracked black pepper to taste: Essential seasoning to brighten and balance all flavors.
1 cup petite lentils (French Le Puy or black Beluga lentils): Tender, yet firm lentils provide great texture and nutrition.
2 quarts (8 cups) low sodium beef broth or stock: Creates a hearty and flavorful soup base that complements the lentils and onions.
6 to 8 sprigs fresh thyme (or 1 tsp. dried thyme): Adds an earthy and floral note that pairs beautifully with onions.
1 bay leaf: Brings subtle herbal fragrance to the simmering pot.
2 Tbsp. sherry vinegar: Brightens the soup with a touch of acidity to balance the sweetness.
8 to 12 (½-inch) slices French bread (from 1 baguette): Creates the perfect crispy, toasted topping once broiled with cheese.
1 1/2 cups grated Gruyère cheese: Melts into a golden, bubbly crown that adds creaminess and a savory finish.

How to Make French Onion Lentil Soup Recipe

Step 1: Caramelize the Onions

Start by melting butter and olive oil together in a large Dutch oven over medium heat. Add the thinly sliced onions with half a teaspoon of salt and cook slowly, stirring every few minutes, until they turn a deep golden brown. This caramelization is the heart of the soup, transforming simple onions into a sweet, rich base. It takes about 40 minutes, so patience here will pay off hugely! In the last couple of minutes, stir in minced garlic and tamari for an added boost of flavor.

Step 2: Add Lentils and Broth

Next, stir in the lentils along with the beef broth, thyme sprigs, bay leaf, and freshly cracked black pepper. Bring the mixture to a low boil, then reduce the heat, leaving the pot lid slightly ajar to let steam escape. Simmer gently for about 30 minutes, or until the lentils are tender but not mushy. Once cooked, remove the bay leaf and thyme sprigs, then stir in the sherry vinegar to brighten the flavors. Adjust salt and pepper if needed – this step really fine-tunes the taste balance.

Step 3: Prepare the Topped Bowls

Preheat your broiler to high. Ladle the hot soup into ovenproof bowls placed on a baking sheet. Top each bowl with slices of French bread, then sprinkle generously with grated Gruyère cheese. Place the baking sheet under the broiler about 6 inches away from the heat and broil for 2 to 4 minutes until the cheese bubbles and turns a beautiful golden brown. Keep a close eye so the cheese melts perfectly without burning. Serve right away while it’s warm and irresistible.

How to Serve French Onion Lentil Soup Recipe

A white ceramic bowl with a handle is filled with a dark brown soup with pieces of tender cooked onions and small round brown lentils. Two slices of toasted bread float on top, each covered with melted pale yellow cheese that is slightly browned and bubbly with a sprinkled touch of black pepper and herbs. A gold spoon is lifting a scoop of lentils and translucent onion strands from the bowl. The bowl sits on a white marbled surface, alongside a piece of crusty light brown bread and some loose shredded cheese. In the background, there is a glimpse of another similar bowl and some green herb sprigs. Photo taken with an iphone --ar 4:5 --v 7

Garnishes

A sprinkle of fresh thyme leaves or a few twists of freshly cracked black pepper on top adds a lovely herbal touch and visual appeal. You can also add a drizzle of extra virgin olive oil if you like a hint more richness.

Side Dishes

This soup pairs wonderfully with a crisp green salad dressed in lemon vinaigrette or a plate of roasted veggies. Since the soup is full-flavored and hearty, lighter sides help create a well-rounded meal.

Creative Ways to Present

For a charming presentation, serve the soup in mini cast-iron pots or rustic crockery. Layer the bread and cheese toppings just before serving to keep them crisp. You could even turn this into a fun interactive meal by letting guests add their own bread and cheese before broiling at the table.

Make Ahead and Storage

Storing Leftovers

Store any leftover soup in an airtight container in the refrigerator for up to 3 days. Keep the bread and cheese topping separate until ready to reheat, to prevent sogginess.

Freezing

This French Onion Lentil Soup Recipe freezes beautifully. Cool the soup completely, then transfer to freezer-safe containers. Freeze for up to 3 months. It’s best to freeze without the bread and cheese; add those fresh when you reheat.

Reheating

Reheat the soup gently on the stove over medium heat, stirring occasionally. When warmed through, ladle into ovenproof bowls, add fresh bread and Gruyère, then broil as usual until bubbly and golden. This way, you experience that delightful cheese crust every time.

FAQs

Can I make this soup vegetarian?

Absolutely! Substitute the beef broth with a rich vegetable broth, and consider adding a splash of soy sauce or tamari to maintain that umami depth.

What kind of lentils work best?

French Le Puy lentils or black Beluga lentils hold their shape beautifully and add a lovely texture to the soup, but any small, firm lentil will do.

Is it necessary to use Gruyère cheese?

Gruyère offers a nutty, melty quality that’s perfect here, but Swiss or even a mild cheddar can be used as alternatives if needed.

Can I prepare the caramelized onions ahead of time?

Yes! Caramelized onions can be made up to 2 days in advance and refrigerated. Just warm them gently before continuing with the recipe.

How do I avoid burning the cheese under the broiler?

Watch closely during broiling and keep the bowls a few inches away from the heat source. It usually takes 2-4 minutes, so stay nearby to prevent burning.

Final Thoughts

This French Onion Lentil Soup Recipe is a wonderful way to bring cozy comfort and sophisticated flavor into your kitchen with everyday ingredients. It’s perfect for sharing with loved ones or savoring on your own when you want a nourishing, soul-soothing meal. Give it a try and you might just find your new favorite soup to return to season after season.

French Onion Lentil Soup Recipe

Ingredients You’ll Need