How to Make It
In an unheated, large heavy-bottomed saucepan, combine the olive oil and garlic and stir to coat the garlic with the oil. Place over moderate heat and cook until the garlic is fragrant, about 2 minutes. Do not let it brown. Add the beans, stir to coat with oil, and cook for 1 minute more. Add 1 quart (1 l) of homemade chicken stock, the bay leaves, sage and 2 teaspoons of fine sea salt. Cover, bring to a simmer over moderate heat. Simmer gently until the beans are tender, about 25 minutes. Stir from time to time to make sure the beans do not stick to the bottom of the pan. The beans should just be covered with liquid. Add additional stock if necessary. (Cooking time will vary according to the freshness of the beans.) Taste for seasoning. Remove and discard the bay leaves, onion, and sage leaves.
Set a large sieve over a large bowl. Transfer the beans and liquid to the sieve to drain. Transfer 2 cups (50 cl) of the beans and all of the drained liquid to a food processor. Purée. Add the mustard to the purée and pulse to blend. Return the drained beans and the purée to the saucepan. Reheat gently at serving time. Pass a cruet of extra-virgin olive oil to drizzle over the beans.
Rinse the beans, picking them over to remove any pebbles. Place the beans in a large bowl, add boiling water to cover, and set aside for 1 hour. Drain the beans and proceed with the preparation for fresh beans, simmering for about 1 hour. (Cooking time will vary according to the freshness of the beans.)