How to Make It
In a large pot, heat the oil over moderate heat. Add the onion, garlic, and carrots and cook, stirring occasionally, until the vegetables start to soften, about 10 minutes.
Add the lentils, water, salt, bay leaf, and red-pepper flakes to the pot. Bring to a boil. Reduce the heat and simmer, partially covered, stirring occasionally, for 15 minutes. Add the linguine and simmer, stirring occasionally, until the lentils are tender and the pasta is done, 15 to 20 minutes longer.
Stir the black pepper and the parsley into the soup. Top each serving with some of the grated Parmesan.
• Substitute one chopped fennel bulb for the carrots.
• Stir one-and-a-half cups of spinach, cut into very thin strips, into the soup along with the parsley.