Separate garlic heads into cloves (do not peel). Pick over beans and in a 4-quart kettle combine with garlic and enough cold water to cover beans by 2 inches. Gently simmer bean mixture, adding more water as necessary to keep beans covered, until beans are tender, about 1 1/2 hours. Drain bean mixture in a colander. Remove garlic and peel. In a small bowl mash garlic with a fork and gently stir into beans.
Preheat oven to 400 degrees. In a 2-quart nonreactive baking dish gently stir together bean mixture, broth, and salt and pepper to taste. In a bowl with your fingertips blend together bread crumbs and butter. Sprinkle crumb mixture evenly over bean mixture and bake in middle of oven until golden and bubbly, about 20 minutes
Recipe courtesy of Gourmet Magazine