In an enameled cast-iron casserole, heat the oil. Add the celery, onion and leek and cook over moderately high heat, stirring a few times, until softened, 5 minutes. Add the farro and tomato paste and cook, stirring, until the grains are coated and shiny, 30 seconds. Add 1 quart of the water and the beans and bring to a boil. Simmer over low heat for 30 minutes. Add the carrots and the remaining 1 quart of water. Cover and cook over low heat until the carrots are tender, 30 minutes. Add the peas, cover and cook until tender, 5 minutes. Season with salt and pepper, top with the basil and serve with Juniper Grissini.