French Lentil Soup with Potatoes

French lentil soup is named for its lentils. French green lentils are small and dark, mottled green-gray, and they keep their shape after a long simmer instead of breaking down into a purée. Here they cook in one pot with onion, carrots, celery, tomato paste, thyme, and bay leaves, along with chunks of Yukon Gold potato that go tender and a little creamy at the edges. Mashing a few of those potato pieces at the end thickens the broth without a blender, and a spoonful of red wine vinegar just before serving lifts the earthy flavor.

This is a French-inspired vegetarian soup, not a traditional regional recipe. A little smoked paprika and cumin stand in for the smoky depth that bacon or ham would otherwise bring. Plan on about 1 hour 10 minutes from start to finish. It makes about 11 cups, enough for 6 hearty bowls.

Jump to Recipe

Ingredient Notes

The full quantities are in the recipe card below. These are the choices that most affect texture and seasoning.

• French green lentils: You’ll see them sold as French green lentils, French lentils, Puy lentils, or lentilles du Puy. Lentilles du Puy is a protected name for lentils grown around Le Puy in France. Other French green lentils are the same small type grown elsewhere, including in North America, and they work the same way here. Pick out any small stones, rinse, and drain them. You don’t need to soak them.
• Yukon Gold potatoes: Their medium starch content lets them hold their shape through the simmer but still mash easily against the side of the pot. Cut them into 3/4-inch pieces. Smaller pieces fall apart before the lentils are done, and much larger ones can still be firm. The skins are thin, so peeling is up to you.
• Low-sodium vegetable broth: Sodium varies a lot from brand to brand, and six cups of a regular broth can make the soup salty before you’ve added anything. With low-sodium broth, the teaspoon of salt in the recipe gives you a base you can adjust at the end.
• Kosher salt: The measurement is for Diamond Crystal. Morton kosher salt and table salt pack more salt into each spoonful, so start with 1/2 teaspoon of either and add more after tasting.
• Herbs and spices: Thyme is the main herb. Crumble the dried rosemary between your fingers as it goes in so the needles soften in the broth. The smoked paprika and cumin are there for warmth, not heat. For a more herb-forward soup, leave out the cumin.
• Red wine vinegar or lemon juice: Lentil soup can taste flat without acid. Vinegar gives a rounder, slightly fruity tang, and lemon juice tastes fresher. Add either one off the heat at the end, so it stays bright.

How to Make French Lentil Soup

1. Build the base gently

Cook the onion, carrots, and celery over medium heat until the onion is soft and translucent. You want them softened, not browned. Then cook the garlic and tomato paste, stirring, until the paste darkens from bright red to brick red and starts to coat the bottom of the pot. That bit of browning adds the savory depth a meatless broth needs. The dried herbs and spices go in last, for about 30 seconds in the hot oil, which wakes up their flavor before the liquid goes in.

2. Simmer the lentils and potatoes together

The lentils, potatoes, broth, and water all go in at once. With the potatoes cut to 3/4 inch, they turn tender in about 20 minutes, and the lentils catch up 10 to 15 minutes later. Keep the soup at a gentle simmer with the lid slightly ajar. A hard boil splits the lentil skins and wears the potatoes down. Start tasting at 25 minutes. The lentils are done when they’re soft and creamy inside but still hold their round shape. Older lentils can take 40 minutes or a little longer.

3. Adjust the body

Take out the bay leaves, then press 6 to 8 potato pieces against the side of the pot and stir them in. The mashed potato thickens the broth slightly and makes it a little creamy. The finished soup should be thick and hearty, with lentils and vegetables in every spoonful and enough broth to ladle easily. If it looks more like a stew, add water, 1/2 cup at a time.

4. Finish with acid, then salt

Stir in the vinegar or lemon juice off the heat and taste before you add more salt. The acid brightens the soup, so it may need less salt than you’d expect. If it still tastes flat, add salt in small pinches, or another teaspoon of vinegar.

Tips for the Right Texture

• Expect it to thicken. The lentils and potatoes keep absorbing broth as the soup sits, and even more overnight. Leftover soup often needs 1/4 to 1/2 cup of water or broth for every 2 cups when you reheat it.
• Lentils still firm at 40 minutes? Older dried lentils take longer. Keep simmering and check every 5 minutes, adding hot water if the pot gets too thick.
• Potatoes falling apart? The pieces were cut too small, or the soup boiled instead of simmering. It still tastes good. The broth will just be thicker and cloudier.
• Tastes flat? Add acid and salt before anything else. A teaspoon more vinegar usually does more than extra herbs.

Substitutions and Variations

• Brown or regular green lentils: Use the same amount and start checking after 20 minutes. They soften more than French lentils, so the broth comes out thicker and less clear.
• Black (beluga) lentils: These also hold their shape and cook in a similar time. Don’t use red or yellow lentils, which break down into a purée.
• Fresh herbs: Use 1 tablespoon fresh thyme leaves in place of the dried thyme, and 1 1/2 teaspoons finely chopped fresh rosemary in place of the dried rosemary.
• Greens: Stir in 4 cups of baby spinach during the last 2 minutes, or 3 cups of chopped kale (stems removed) during the last 8 minutes. Add a splash of water if the soup gets too thick.
• Leeks: Replace the onion with 2 medium leeks, white and light green parts only, thinly sliced and well rinsed.
• Red potatoes: These hold their shape like Yukon Golds. Russets are starchier and tend to break down during a 30-minute simmer.

What to Serve with French Lentil Soup

Crusty bread or toasted baguette slices, a green salad with a mustardy vinaigrette, or a drizzle of good olive oil over each bowl. A little grated Parmesan works too, if you don’t need the soup to stay vegan. For another meatless pot with beans and potatoes, try our vegetarian cowboy bean soup. Our fall soup recipes collection and the soups section have more ideas.

Storage, Reheating, and Freezing

• Refrigerate: Cool the soup and refrigerate it in airtight containers within 2 hours of cooking. It keeps for 3 to 4 days.
• Reheat: Warm it in a saucepan over medium heat, adding water or broth to loosen it, and stir until it’s steaming hot all the way through (165°F). Taste again: a small splash of vinegar brings back the brightness.
• Freeze: Freeze in airtight containers, leaving about 1 inch of headspace, for up to 2 to 3 months for best quality. The lentils and broth freeze well. The potato pieces soften and can turn slightly grainy after thawing. If you’re cooking a batch mainly for the freezer, leave out the potatoes and simmer fresh 3/4-inch potato pieces in the reheated soup for about 15 to 20 minutes, adding water as needed. Thaw in the refrigerator overnight, or reheat from frozen over low heat, stirring often.

French Lentil Soup FAQ

Should I soak French green lentils first?

No. Rinse them and pick out any debris. Unsoaked French green lentils cook through in about 30 to 40 minutes in this soup.

Is this soup vegan?

Every ingredient is plant-based, so it’s vegan as long as your vegetable broth is. Skip the Parmesan if you serve it with a topping.

Can I use canned lentils?

Yes, though the lentils will be softer. Use three 15-ounce cans of lentils, drained and rinsed, cut the broth to 5 cups, and leave out the water, since canned lentils don’t absorb much liquid. Simmer the vegetables and potatoes in the broth for about 20 minutes, until the potatoes are tender. Then add the lentils and simmer for 10 minutes more before finishing as written.

Recipe Card