Place beans in saucepan and add enough water to cover by 2 inches/5 cm; let soak for 8 hours or overnight. (Or bring to boil; boil for 3 minutes. Remove from heat; cover and let soak for 1 hour.)

Discarding soaking liquid, drain. Place in saucepan with 8 cups/2 L water. Bring to boil; reduce heat and simmer until tender, 30 to 45 minutes. Reserving cooking liquid, drain. Add enough water to cooking liquid to make 7 cups/1.75 L; set aside.

Sprinkle cod all over with half of the salt; refrigerate for at least 30 minutes or for up to 4 hours. Rinse under cold water and pat dry; cut into chunks. Discarding stems, pull off collard leaves and coarsely chop.

Meanwhile, in stockpot, heat oil over medium-low heat; cook leek and onions, stirring often, until tender, about 10 minutes. Increase heat to medium; add potatoes and parsley. Cook, stirring, until parsley is wilted, 2 to 3 minutes.

Add beans, reserved liquid, pepper, cayenne and remaining salt; bring to boil. Add collards and return to boil; reduce heat and simmer, covered, until collards are softened, about 30 minutes.

Add cod; over low heat, poach until fish flakes easily, 4 to 5 minutes. Ladle into individual serving bowls and drizzle with olive oil (if using). Serve with lemon wedges.

Makes 6 to 8 servings.