Vegetarian French onion soup meets lentil soup with this delicious French Lentil Soup recipe.  This is the best lentil soup with all the flavors we love about French onion soup with added lentils for a more substantially filling and protein rich vegetarian soup. 

bowls of French lentil soupThis vegetarian soup makes a hearty main or you can serve it as a starter.  If you’re like me and love good healthy soup recipes, especially during chilly winter months, I know you’ll enjoy this French Lentil Soup recipe as much as I do!

bowls of French lentil soup ingredients

Best Lentil Soup Recipe

This is the best lentil soup recipe! We use many of the same ingredients that you’d use to make a vegetarian French onion soup, then add in some lentils. So good!

  • Onions (I like to use a mix of sweet onion and red onion)
  • Garlic
  • Butter (you can also use vegan butter or extra-virgin olive oil)
  • Bouquet garni (fresh parsley and thyme and dried bay leaves)
  • Vegetable broth
  • Worchestershire sauce 
  • Bread (optional)
  • Parmesan cheese 
  • Lentils

Variations

  • Pour in 1/2 cup sherry or wine (red or white) to deglaze the onions
  • Garnish with Gruyere cheese instead of Parmesan

How to Make French Lentil Soup

This starts out as a vegetarian French onion soup with lots of caramelized onions then we add in some lentils. This combo makes the best lentil soup recipe!

  1. Caramelize onions.  Melt butter in a large soup pot or Dutch oven over medium low heat.  Add onions, sprinkle with a pinch of salt, and cook for 40 minutes until onions are soft and caramelized. Add garlic the last 2-3 minutes of cooking.
  2. Add broth and herbs. Pour in broth, lentils, bay leaf and sprigs of thyme and parsley.
  3. Simmer.  Bring to a boil, then place lid on pot and reduce heat to a low simmer for 40-45 minutes until lentils are tender.
  4. Make toasties. Arrange baguette slices brushed with olive oil on a baking sheet in a single layer. Bake for 1-2 minutes then remove from oven and sprinkle with grated Parmesan cheese and bake another 2-3 minutes until melted.
  5. Serve. Ladle soup in bowls and float 2-3 Parmesan toasties on top.

sliced onions

Best Onions for French Onion Soup

The best onions to use for vegetarian French onion soup are yellow onion, sweet onion (such as Vidalia and Walla Walla) and red onion.

  • Yellow onion. Yellow onions are probably the most commonly used onion.  They’re great grilled or simmered in soups and stews.
  • Sweet onions.  Sweet onions (Vidalia and Walla Walla) have a little less of a bite to them than the yellow or white onion, and they taste a little on the sweet side.
  • Red onions. Red onions are similar in flavor to the rustic yellow onion.  

How to Caramelize Onions

This is probably the most important part of a good onion soup. Caramelizing 3-4 onions can typically take up to an hour, but we cut down on time just a bit for this soup and we caramelize the onions for about 40 minutes.

  1. Slice onions. Trim the tip and root from onions.  Cut the onions in half and remove the skins.  Cut each half into thin slices.
  2. Heat butter. Melt butter in large skillet over medium low heat. Or if using olive oil, heat oil over medium low heat.
  3. Add sliced onions. Add all of the sliced onions to the pan and stir them to coat with melted butter or olive oil.
  4. Cook. Cook the onions and check every 5-7 minutes. As the onions cook, stir and scrape any onion glaze (fond) that forms at the bottom of the pan. As the onions start to soften, there will be liquid in the pan. After about 20 minutes, the onions will turn blonde and become sticky and you’ll see some of the glaze (fond) building up at the bottom of the pan. Towards the end of the process, the onions will turn a darker brown color and release a delicious aroma.

Tips for Caramelizing Onions

  • The best pans for caramelizing onions is a good stainless steel or cast iron skillet.  You can use a non-stick pan, but the onions just don’t caramelize quite as nicely.
  • Caramelizing onions is a process that breaks down the sugars in the onions giving the onions a deep rich flavor. It’s really as simple as melting some butter (you can also use vegan butter or olive oil) and adding the thinly sliced onions to the pan along with a pinch of salt.
  • Don’t over-crowd the pan.  Depending on the size of your pan, it’s best to caramelize 3-4 onions at a time.
  • Cook the onions slowly on low heat until they turn a rich mahogany brown in color.
  • Once the onions start to cook, be sure to check on them every 5 – 7 minutes to stir them.  Scrape the sticky glaze (fond) that builds up on the bottom of the pan and stir it into the onions.  Lots of flavor in the fond!
  • The onions will start to dry at the end of the caramelization process. You can deglaze the pan with either water, broth, sherry or wine.

What Cheese Goes on French Onion Soup

Classic onion soup is traditionally topped with crusty bread and sliced or shredded Gruyere cheese.  I’ve kept things simple (and lower in calories and fat) by garnishing this soup with Parmesan cheese, but feel free to go with Gruyere cheese or no cheese at all if you like.

pot of vegetarian soup

What Are the Best Lentils to Use

There’s a variety of different types of lentils to cook with, such as green lentils (also called French lentils or Le Puy lentils), red lentils, black lentils (also called beluga lentils) and brown lentils.  I find that Le Puy lentils (also called French Green Lentils) or just plain green lentils and brown lentils are the best lentils to use when making lentil soup with because they tend to hold their shape better and retain a slightly firmer texture.  They take about 40-45 minutes to cook cook. 

Health Benefits of Onions

  • Improves immunity.  Onions are a rich source of both vitamin C and phytochemicals which helps to strengthen our immune systems.  Vitamin C is an essential water-soluble vitamin that our bodies need to make collagen.  Collagen is a type of protein that plays a role in wound healing and immunity support. 
  • Regulates blood sugar levels. Onions are a rich source of  biotin.  Besides being good for healthy skin and hair, biotin has many positive impacts on our health, one of which is combatting symptoms associated with type 2 diabetes.  A combination of biotin and chromium may help to improve regulating blood sugar levels and even decrease insulin resistance.
  • Lowers cholesterol.  Raw onion also promotes production of HDL, which is the good cholesterol that’s needed for optimal health, and reducing the risk of heart attack and stroke.
  • Lowers blood pressure. The sulfur found in onions acts as a natural blood thinner and it prevents blood platelets from clotting, which may help to lower blood pressure and the risk of heart attack or stroke.  The powerful antioxidant Quercetin found in onions may also help to reduce the risk of  heart attack and stroke by preventing  plaque buildup in our arteries.

bowls of French lentil soup

Health Benefits of Lentils 

  • Heart healthy. Lentils are low in fat, high in protein, they’re a good source of iron, fiber, folic acid and magnesium. 
  • Improves immunity. They’re also rich with polyphenols.  Polyphenols are compounds found in plant foods (such as fruits, vegetables, herbs, spices, dark chocolate, wine and tea), and they act like antioxidants neutralizing free radicals and help to reduce inflammation which is linked to chronic disease. 
  • Nutrition. One cup of cooked lentils provides approximately 18 grams of protein, 40 grams of carbohydrates and 140 calories.

bowls of lentil soup

Easy Lentil Recipes

More Vegetarian Soup Recipes

Bowls of French Lentil Soup
Yield: 8 servings

French Lentil Soup

Prep Time 10 minutes
Cook Time 1 hour 30 minutes
Total Time 1 hour 40 minutes

Vegetarian French onion soup meets lentil soup with this delicious French Lentil Soup recipe.  This is the best lentil soup with all the flavors we love about French onion soup with added lentils for a more substantially filling and protein rich vegetarian soup. 

Ingredients

  • 2 tablespoons extra-virgin olive oil
  • 4 cups onion, thinly sliced (about 2 sweet onions and 2 red onions)
  • 1-2 garlic cloves, peeled and minced
  • 12 cups vegetable broth
  • 1-2 tablespoons Worcestershire (optional)
  • 1 cup dried green lentils
  • 1 bay leaf
  • 1 sprig fresh thyme
  • 2-3 sprigs parsley
  • 1/2 cup parsley, chopped

Cheese Toasties

  • Baguette slices
  • Olive oil
  • Parmesan cheese or Gruyere cheese

Instructions

  1. Melt butter in a large soup pot or Dutch oven over medium low heat.
  2. Add onions, sprinkle with a pinch of salt, and cook for 20 minutes until onions are soft and caramelized. Stir in and saute the minced garlic the last 2 minutes of cooking onions.
  3. Stir in 1-2 tablespoons Worcestershire sauce to the onions.
  4. Pour in broth, lentils, bay leaf and sprigs of thyme and parsley.
  5. Bring to a boil, then place lid on pot and reduce heat to a low simmer.
  6. Simmer for 40-45 minutes or until the lentils are tender.
  7. Remove bay leaf and thyme and parsley.
  8. Arrange baguette slices brushed with olive oil on a baking sheet in a single layer. Bake for 1-2 minutes then remove from oven and sprinkle with grated Parmesan cheese and bake another 2-3 minutes until melted.
  9. Ladle soup in bowls and float 2-3 Parmesan toasties on top.
  10. You can also ladle soup into bowls, top each with 2-3 slices of bread and top with cheese. Put soup bowls into the oven to melt cheese and toast baguette.

Notes

VARIATIONS

  • Pour in 1/2 cup sherry to deglaze the onions
  • Garnish with Gruyere cheese instead of Parmesan

Nutrition Information:

Yield:

8

Serving Size:

1

Amount Per Serving: Calories: 235Total Fat: 10gSaturated Fat: 4gTrans Fat: 0gUnsaturated Fat: 6gCholesterol: 15mgSodium: 1183mgCarbohydrates: 26gFiber: 4gSugar: 8gProtein: 10g

theharvestkitchen.com attempts to provide accurate information, however, this nutritional information is provided as a courtesy and is an estimate only. The nutritional information provided comes from online sources and calculations.