I love a lentil soup with a vinegary bite, and my vinegar of choice is 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. I don't use a whole can of crushed tomatoes, so you should freeze the leftovers for another time.
1/4 cup olive oil
1 onion diced, about 1 1/2 cups
2 carrots peeled and diced, about 1 1/2 cups
4 cloves garlic, thinly sliced
2 teaspoons ground cumin
1 teaspoon curry powder
pinch red pepper flakes
1 teaspoon kosher salt, plus more to taste, and freshly ground black pepper
1 cup red lentils, picked over and rinsed
4 cups cooked chickpeas, or two 15-oz cans, drained
1/4 cup white balsamic vinegar or lemon to taste, see headnote
2 cups crushed canned or jarred tomatoes
4 cups vegetable or chicken stock or water
In a large pot, place the oil, onion, carrots, garlic, cumin, curry, red pepper flakes, fresh pepper, and a 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 the mixture is simmering. Simmer, covered, 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.