I made a few modifications to the original recipe based on what I had on hand:
Cumin: I prefer starting with whole seeds, which I crush in a mortar and pestle, but pre-ground is fine, too.
I love a lentil soup with a vinegary bite, so in place of the lemon juice, I used 1/4 cup white balsamic vinegar. You could use red wine, white wine, cider vinegar in its place. The soup does not take vinegary in the end, but there is a welcomed sharpness. You, of course, could stick to lemon, in which case, add it at the very end to taste.
I had cooked chickpeas on hand, so I added them, and I really like the combination of the lentils, which break down completely, and the chickpeas, which hold their shape and add nice texture. I had cooked 1/2 a pound, which yielded about 4 cups. When I made it the second time, I used two cans, drained.
I prefer the soup a little less tomato-y, so I use 2 cups crushed tomatoes, but use a whole can (28 oz) as the original recipe suggests if you wish. I like the Pomi brand crushed tomatoes.
Original recipe calls for adding chard or collard greens at the end, which I am sure would be delicious, but if you don't have them on hand, don't feel the need to run out. Original recipe also calls for puréeing some of the soup at the end, but I kind of like it as it is with all of the various textures — purée if you wish.
6 to 8
onion diced, 1.25-1.5 cups
carrots peeled and diced, 1.25-1.5 cups
cloves garlic, thinly sliced
ground cumin, see notes above
pinch red pepper flakes
kosher salt, plus more to taste
fresh pepper to taste
cooked chickpeas, or two 15-oz cans, drained
white balsamic vinegar or lemon to taste, see notes above
In a large pot, place the oil, onions, carrots, garlic, cumin, curry, red pepper flakes, fresh pepper, and pinch of salt. Bring to a sizzle over high heat, then reduce the heat to medium and cook, stirring occasionally to coat the vegetables in the spices, about 10 minutes.
Add the lentils, chickpeas, 1 teaspoon salt, vinegar, crushed tomatoes, 4 cups stock or water plus 2 more cups of water. Bring to a boil, then reduce heat so mixture is simmering. Simmer for 30 minutes or longer, until the lentils have broken down, and the mixture has thickened. Taste. Adjust seasoning with more salt (I usually add another teaspoon or more of kosher salt, but adjust as you see fit), pepper, or vinegar/lemon to taste. Serve with bread.