- 3 tablespoons olive oil
- 1 medium onion, finely chopped
- 2 medium carrots, finely chopped
- 1 celery rib, finely chopped
- 1 1/4 cups lentils (preferably French green)
- 6 cups water
- 1 1/2 teaspoons salt
- 1/4 teaspoon black pepper
- 4 oz smoked sausage
- 1 tablespoon balsamic vinegar, or to taste
- Heat 2 tablespoons oil in a 4-quart heavy pot over moderately high heat until hot but not smoking, then sauté onion, stirring occasionally, until golden brown, about 6 minutes. Add carrots and celery and cook, stirring, until softened, about 5 minutes. Add lentils, water, salt, and pepper and bring to a boil, then reduce heat to moderate and cook, covered, until lentils are tender, about 30 minutes.
- While lentils are cooking, heat remaining tablespoon oil in a 10-inch nonstick skillet over high heat until hot but not smoking, then brown sausage on all sides, about 5 minutes. Cool sausage slightly on a cutting board, then cut into 1/2-inch-thick pieces. Add sausage to soup and stir in vinegar.