Add the olive oil to a large, cast-iron pot or Dutch oven and heat over medium. Once shimmering, add in the diced yellow onion, diced carrots (no need to peel), and diced celery. Cook, stirring frequently, 5–7 minutes. Add in garlic, stir, and cook for 1 minute. Add diced potatoes (again, no need to peel) and diced sweet potatoes (I do peel these). Stir to coat everything in the oil and cook for 3 minutes.
Add tomato paste and all seasonings: ground cumin, Italian seasoning, yellow curry powder, ground turmeric, paprika, and salt and pepper to taste. Stir, toasting the seasonings and coating all the veggies. Cook for 2 minutes. Add undrained fire-roasted diced tomatoes and undrained fire-roasted crushed tomatoes. Cook 2–3 more minutes, stirring frequently, to bring out all the flavors.
Rinse the lentils in cold water in a fine mesh sieve. Add lentils, vegetable broth, and chicken stock (or additional vegetable broth) into the pot. Stir in the bay leaves.
Increase heat and bring the soup to a boil. Once boiling, you’ll see some bubbles or froth at the top of the pot. Skim this off with a spoon and discard. Stir, then reduce heat to medium low so the soup is gently simmering. Partially cover the pot with a lid, leaving some room for steam to escape. Cook 25–30 minutes or until lentils are tender (they should still hold their shape).
Optional (creamier texture): Transfer 2 cups of the soup to a high-powered blender. Securely fasten the lid and blend until smooth (watch out for steam!). Pour the blended soup back into the pot and stir. I occasionally do this, but also enjoy the texture of all the veggies—up to you!
Remove the pot from heat and add 1/2 teaspoon lemon zest and 1 tablespoon lemon juice. Taste and adjust seasonings; add additional lemon juice if desired, salt and pepper if needed, and/or a pinch of red pepper flakes. Stir in the freshly chopped parsley.
Serve while hot. Top individual bowls with freshly grated Parmesan cheese. Leftovers will keep (stored properly in an airtight container) for about 4–5 days in the fridge.
Video
Notes
Tips:
Thin the soup. I like this soup thick and hearty, but if you’d like it thinner, add some additional vegetable broth or stock.
Skim the surface of the soup. When cooking lentils, a froth will rise to the top. I like to skim this off with a spoon; this makes the lentils easier to digest. The froth forms as a result of lentils releasing gas and enzymes as they cook.
Take your time. This soup requires quite a few ingredients to sauté and toast before it can be left alone to simmer. Take your time sauteing the aromatics, toasting the spices, and sauteing the tomatoes; these steps add layers of flavor.
Don’t forget the fresh ingredients. The freshly chopped parsley, lemon zest, and lemon juice truly make all the flavors in the soup sing; I wouldn’t recommend leaving any of these ingredients out.
Finely dice or chop the veggies. In order for everything to cook in the right time, we want the onion, celery, and carrot finely diced. The potatoes also need to be chopped small—1/2-inch or smaller cubes. The more evenly cut the veggies are, the more evenly they’ll cook (we don’t want some mushy and some hard).
Storage: Store leftovers in an airtight container for 4–5 days in the fridge.