- 2 tablespoons olive oil
- 1 large yellow onion, diced
- 2 stalks celery with leaves, diced
- 2 carrots, diced
- 1 1/2 teaspoons minced garlic
- 6 cups water
- 2 cups French green lentils
- 2 tablespoons chopped fresh parsley
- 1 tablespoon salt, or more to taste
- 1 tablespoon ground coriander
- 1 tablespoon ground cumin
- 1 1/2 teaspoons ground black pepper
- 1/2 teaspoon cayenne pepper
- 1/4 cup butter (optional)
- 1 cup all-purpose flour (optional)
- 1 lemon, cut into wedges
- 2 tablespoons chopped fresh parsley
- freshly ground black pepper
- Heat olive oil in a large heavy-bottomed pot over medium heat. Cook and stir onion, celery, and carrots until slightly tender, about 5 minutes. Add garlic; cook and stir until fragrant, 30 seconds. Add water, lentils, 2 tablespoons fresh parsley, salt, coriander, cumin, black pepper, and cayenne pepper; stir to incorporate. Cover and simmer until lentils are tender, stirring occasionally, 1 1/2 hours.
- Whisk butter and flour together in a small saucepan over medium-low heat; stir constantly until thickened and paste-like, about 10 minutes. Reduce heat to low, stirring every 2 to 3 minutes, until light brown, about 20 more minutes. Whisk flour paste into finished soup, a spoonful at a time, until smooth and creamy. Serve with lemon wedges, 2 tablespoons parsley, and a sprinkle of freshly ground pepper.