Makes 10 cups, to serve 8.
1 tablespoon olive oil
1 medium onion, chopped (1½ cups)
2 medium carrots, peeled and chopped (1 cup)
1 celery stalk, chopped (½ cup)
1 red bell pepper, seeded and chopped (1 cup)
1 cup green or black lentils
3 garlic cloves, minced
½ teaspoon freshly ground black pepper
8 cups low-sodium vegetable broth
2 tablespoons chopped fresh parsley
1 bunch sorrel (or 5 ounces baby spinach plus 1 tablespoon fresh lemon juice and ½ teaspoon lemon zest)
In a stockpot, heat the olive oil over medium-high heat. Add the onion, carrots, celery, and bell pepper and sauté until the onion becomes translucent, about 10 minutes.
Add the lentils, garlic, and black pepper; cook for 1 minute more. Add the broth and bring to a boil. Reduce the heat to maintain a simmer and cook for 20 to 25 minutes, until the lentils are tender.
Stir in the parsley and sorrel; cook until wilted, 2 to 3 minutes. Serve.