Lentil Soup

Three things make this vegetarian lentil soup so good: caramelized onions, toasted tomato paste (it's easy!), and lots of carrots and celery. Make a big pot to have some now and save some for later—this soup is freezer friendly!

Homemade lentil soup with kale, carrots and tomato paste in a bowl with a spoon.
Sally Vargas

When I learned to cook, my first challenge was to make a five-gallon pot of lentil soup. Yes, you heard that right, five gallons!

I still laugh when I remember standing over a giant pot on a giant restaurant stove adding one pinch of salt at a time when a quarter of a cup or so would have been closer to the mark. That lentil soup became a vegetarian staple in our restaurant.

Since then, I’ve tweaked it to make it even more flavorful. Carrots and celery added to the mix, along with caramelized onions and tomato paste, bring forth an even tastier bowl, which vegetarians and carnivores alike can relish with gusto.

To top it off, I stir in some slivered kale at the end to make a healthy, comforting soup that everyone can enjoy.

I don’t make five gallons anymore, but I still like to make a big pot of this soup and then tuck some away in the freezer for a cold or rainy night.

It will keep for up to 6 months in the freezer. It’s like money in the bank for those dreary fall and winter afternoons when I haven’t shopped and have no intention of doing so.

Easy Lentil Soup in a bowl with a spoon.
Sally Vargas

Video: How to Make Lentil Soup

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Lentil Soup

What Are Lentils?

They are small legumes and range in color from brown to green, red to yellow, and sometimes even black. Along with beans, peanuts, and peas, lentils grow in pods. They’re high in protein and delicious in soups, stews and on their own in vegetarian and spicy Indian dishes, most famously, dal.

Which Lentils Are Best for Lentil Soup?

We chose French green lentils, also known as Le Puy, grown in a region of central France, for this recipe. They are small and dark—almost purple in appearance—and hold their shape during cooking. They also take longer to cook than other varieties.

If you can’t find French lentils, you can substitute almost any other variety. You will need to adjust the water and cooking time to achieve the consistency you want, but this is an ‘eyeball it’ situation—it’s not hard!

Green lentils are our first substitution choice. They are large and flat, and stay fairly firm when cooked. Just cook the soup long enough to soften the lentils—check it every 10 minutes or so after the 20-minute mark.

Brown, yellow, and red lentils are a good next choice. They tend to cook quickly and don’t hold their shape particularly well. If you substitute Puy lentils with any of these, watch them closely. They can easily turn to mush, and you want some shape and texture for this soup.

How to Prep Lentils for Cooking

If you buy lentils from a store bin, it’s a good idea to spread them out on a tray and pick over them and discard any little stones or bits of dirt that could be present. If they seem dusty, rinse them in a colander. Packaged lentils are less likely to contain impurities, but there’s no downside to checking them before cooking.

You don’t need to soak lentils before cooking. But depending on the variety, they can take anywhere from 20 to 50 minutes to soften when simmered in liquid. They absorb their cooking liquid, and many varieties double in size when cooked.

Pot of lentil soup with kale.
Sally Vargas

Flavor Boosters for This Vegetarian and Vegan Lentil Soup

The best way to create depth of flavor for this vegetarian soup is to caramelize the onions, toast the tomato paste and add loads of carrots and celery.

  • Caramelizing onions is simply a process of browning them slowly in the pan. They eventually shrink and become a little sticky, and the sugar in the onions becomes more pronounced. If the bottom of the pan browns before the onions are soft, add water, a tablespoon at a time to scrape up the brown bits—it soon evaporates and helps color and flavor the onions.
  • Toasting tomato paste in the pot is another trick to add intense flavor. It just takes a few minutes of stirring until it turns dark and ruddy.
  • The final trick is to add plenty of carrots and celery. They are the supporting actors and essentially provide the same amount of flavor as vegetable stock would.

Your Food Processor Is a Time Saver.

Pulse the onions in a food processor until they are finely diced. Once you start cooking them, place chunks of carrots, celery, and garlic in the food processor and pulse them together into small pieces.

What to Do With Leftovers

Consider freezing the soup in small one-portion containers so you can pull it out at will, and use for mid-week lunches. This lentil soup recipe will keep for up to six months in the freezer.

What to Serve with Lentil Soup

The beauty of lentil soup is that it can make a hearty meal all by itself. That said, it's nice to have a little accompaniment for variety. You can just serve with a couple of slices of a crusty, hearty bread.

A fresh green salad pairs nicely with lentil soup, as well.

Substitutions and Additions

Make the soup as written and it's both vegan and vegetarian! The subs below may or may not make it more of a flexitarian soup.

  • Use Worcestershire sauce instead of soy sauce (make sure the Worcestershire is vegan if you want to keep the lentil soup vegan).
  • Substitute chicken stock for the water or vegetable stock, if you're not worried about it being vegetarian.
  • Add a little bit of finely diced potatoes or sweet potatoes with the vegetables.
  • For a little heat, you can add some finely chopped jalapeño or serrano pepper.
  • Meat lovers may want to put in some chopped sausage or crumble some bacon on top.
  • Top the soup with some chopped fresh herbs, like cilantro, basil or parsley.

More Great Soup Recipes!

From the Editors Of Simply Recipes

Lentil Soup

Prep Time 15 mins
Cook Time 60 mins
Total Time 75 mins
Servings 6 to 8 servings

To achieve a creamy consistency, I like to puree a little of the soup in the blender and add it back to the pot. Like most lentil soups, this one thickens as it sits. So, be prepared to add more water when you reheat it, or simply enjoy it as a stew.

Ingredients

  • 2 tablespoons olive oil
  • 1 large yellow onion, finely diced
  • 2 tablespoons tomato paste
  • 1 teaspoon dried thyme
  • 1 clove garlic, finely diced
  • 3 stalks celery, finely diced
  • 3 carrots, peeled and finely diced
  • 2 cups (12 ounces) small green French lentils
  • 8 cups water or vegetable stock
  • 1 tablespoon low-sodium soy sauce
  • 1-1/2 teaspoon salt, plus more to taste
  • 1/8 teaspoon pepper, plus more to taste
  • 3 tablespoons lemon juice, plus more to taste
  • 1/2 bunch kale, stemmed and thinly sliced crosswise

Method

  1. Caramelize the onions:

    In a soup pot over medium heat, heat the olive oil. Once the oil shimmers, add the onions and cook, stirring occasionally for 10 minutes, or until deep, golden brown.

    Onions in the bottom of a soup pot for lentil soup.
    Sally Vargas
    Caramelized onions and tomato paste in the bottom of a soup pot.
    Sally Vargas
  2. Cook the tomato paste and vegetables:

    Push the onions to the side of the pot. And in the space you made, add the tomato paste. Stir for 2 to 3 minutes, or until the tomato paste darkens to a ruddy brown. Add the thyme, garlic, celery, and carrots. Cook and stir for 2 minutes.

    Caramelized onions and tomato paste in the bottom of a soup pot.
    Sally Vargas
    Caramelized onions and tomato paste in the bottom of a soup pot.
    Sally Vargas
  3. Add the lentils and liquid, and simmer the soup:

    Add the lentils, 8 cups water, soy sauce, salt and pepper to the pot. Adjust the heat to medium, so the soup is just at a gentle simmer. Simmer for 55 to 60 minutes, or until the lentils are soft.

    Pot of diced vegetables in water.
    Sally Vargas
  4. Finish the soup and serve:

    Scoop out 2 cups of the soup and purée it in a blender until smooth, or use an immersion blender and purée just until the soup takes on a little body and thickens, but you still have texture. Return the blended soup to the pot and stir in the lemon juice. Add the sliced kale and simmer until the kale softens, about 1 to 2 minutes.

    Taste, and add more salt, pepper, and lemon juice, if you like. Serve with a nice slice of crusty bread or a side salad.

    Pot of lentil soup with kale.
    Sally Vargas