Directions

1. 1. Soak the beans in cold water to cover by 2 inches in a large kettle overnight.
2. 2. Cook the leeks in 2 tablespoons of the butter and 2 tablespoons of the olive oil in a large, heavy Dutch oven over moderate heat, stirring frequently, for 30 minutes or until dark golden brown. Add bay leaves, garlic, herbes de Provence, fennel seeds and pepper; cook the mixture, stirring, for 1 minute.
3. 3. Drain the beans and add to leek mixture. Add the stock and bring to a boil. Quickly reduce the heat, and simmer the mixture, partially covered, for 1 hour and 15 minutes or until beans are tender (watch carefully so that the mixture does not boil but stays at a consistent bare simmer.)
4. 4. While the bean mixture is simmering, cook carrots, potato, fennel bulb, and orange zest in remaining 2 tablespoons of butter and remaining 2 tablespoons of olive oil in a large, deep skillet over moderately high heat, stirring often, until the vegetables begin to brown, about 15 minutes.
5. 5. When beans are tender (test by tasting or cutting a bean), stir diced vegetables and tomatoes into soup. Taste for seasoning. Cook soup over moderate heat for 5 minutes. Discard bay leaves.
6. 6. Ladle soup into bowls and serve with Parmigiano-Reggiano and pistou.
7. 7. For the Pistou: Puree 2 cups basil and garlic in a food processor. With the machine running, slowly add the olive oil, continuing until the mixture becomes pasty. Season to taste with salt and pepper and set aside.