Ribollita (Tuscan Vegetable and Bean Soup)

Name: Ribollita (Tuscan Vegetable and Bean Soup)
Prep time: 30 min
Cook time: 45 min
Total time: 1 h 15 min
Cuisine: Italian, European
Ingredients: 1 1/4 cups cooked cannellini beans (8 to 9 ounces); 1/2 cup water or bean canning liquid; 1 small yellow onion; 1 clove garlic; 1/2 stalk celery; 6 sprigs fresh parsley; 3 thin slices pancetta (about 1 ounce); 2 tablespoons olive oil; 1 tablespoon tomato paste; 5 ounces savoy cabbage (about 1/5 small cabbage); 5 ounces flat-leaf kale (about 1/2 bunch); 5 ounces Swiss chard, any color (about 1/2 bunch); 1 medium Yukon Gold or red potato (about 8 ounces); 4 cups water, plus more as needed; 1 1/2 teaspoons kosher salt; 1/2 teaspoon freshly ground black pepper; 4 to 5 ounces crustless stale bread, preferably a crusty white country-style loaf with the crusts trimmed off