This wholesome French stew, similar to Italian minestrone, gets its name and distinctive flavor from pistou, a paste made with crushed basil, garlic, and olive oil. In this recipe, the pistou is embellished with toasted pine nuts, as is pesto.
Make pistou: In the bowl of a food processor, combine basil, pine nuts, garlic clove, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Pulse a few times to combine; with machine running, add 1/2 cup olive oil until mixture is pureed, 1 to 2 minutes. Transfer to a bowl; set aside.
Make croutons: Preheat broiler. Place baguette slices on a baking sheet, and sprinkle each slice with 1/2 teaspoon Parmesan cheese. Place under broiler, and broil until cheese begins to brown, about 2 minutes. Remove from oven; set aside.
Make soup: Tie together thyme, parsley, and bay leaf with kitchen twine to make a bouquet garni. In a 6-quart stockpot, heat 1 1/2 tablespoons olive oil over medium heat. Add 1/2 onion, bouquet garni, and 2 garlic cloves; saute until onion begins to soften, about 4 minutes. Add shelled fava beans; cook 2 minutes more. Add 2 cups water and 1/2 teaspoon salt. Reduce heat to low; cover, and simmer gently 30 to 40 minutes. Transfer beans and cooking liquid to a bowl; reserve, and remove garlic and bouquet garni.
While beans are cooking, bring a medium saucepan of water to a boil; add pasta and 1 teaspoon salt. Cook according to package instructions until al dente. Drain in a colander, and set aside.
In the same saucepan used to cook the beans, heat remaining 1/4 cup olive oil over medium-high heat. Add remaining 1/2 onion with the carrot, celery, leeks, and fennel, and saute 2 minutes. Add remaining 4 cups water, teaspoon salt, and 1/2 teaspoon pepper; cook 5 minutes more. Add peas, zucchini, reserved beans and cooking liquid, and pasta. Bring to a boil, and immediately remove from heat to preserve bright color of vegetables.
To serve, ladle soup into four shallow bowls, and top each with a few croutons. Drizzle 2 tablespoons pistou into each bowl; garnish with Parmesan cheese.