Vegetable Lentil Soup

Family Dinner IdeasDairy-FreeVeganVegetarianLentil

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!

Photography Credit: 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 with changes 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. 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.

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?

I 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 my 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 as 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.

BEST FLAVOR BOOSTERS FOR VEGETARIAN 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. It will keep for up to six months in the freezer.

NEED MORE GREAT SOUP RECIPES?

Vegetable Lentil Soup Recipe

  • Prep time: 15 minutes
  • Cook time: 1 hour
  • Yield: 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
  • 1 tablespoon low-sodium soy sauce
  • 1 1/2 teaspoon salt
  • 1/8 teaspoon pepper
  • 3 tablespoons lemon juice
  • 1/2 bunch kale, stemmed and thinly sliced crosswise

Method

1 Caramelize the onions: In a soup pot over medium heat, add the 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. Caramelized onions and tomato paste in the bottom of a soup pot.

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. Caramelized onions and tomato paste in the bottom of a soup pot.

3 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.

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 for 1 to 2 minutes, or until the kale softens.

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.

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Sally Vargas

Sally Pasley Vargas is a freelance writer and the author of three cookbooks (Food for Friends, The Tao of Cooking, Ten Speed Press, and The Cranberry Cookbook). She currently writes the column The Confident Cook for The Boston Globe along with seasonal recipes for the Wednesday Food Section.

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3 Comments / Reviews

No ImageVegetable Lentil Soup

Did you make it? Rate it!

  1. Brian

    Made this soup tonight and will be putting it in our favorites rotation. Did cheat a bit and used chicken stock vs water, but a veggie stock would have retain the vegan/vegetarian status. Also found the lemon to be enough of an acid hit to brighten the flavor but not be overwhelming. Nice subtle touch!

    xxxxxyyyyy

  2. candace

    I thought this soup was excellent, full of the flavor I expect from a nice hearty bowl of lentil soup. Carmelizing the onions and toasting the tomato paste made all the difference in deeping the flavor. My only additions were a pinch of crushed red pepper and a couple of bay leaves while the soup was simmering. So satisflying on a damp, cool fall night!

    xxxxxyyyyy

  3. Jpp

    This soup is so completely bland! Obviously the soup basics are in the recipe. But the flavor really needs to be ramped up! I added dried oregano and thyme, plus more pepper. The recipe in itself is okay, but if you want a flavorful soup, you really need to put in more herbs.

    xxxxxyyyyy

Vegetable Lentil Soup in a bowl with a spoons.Vegetable Lentil Soup