How to Make It
In a large enameled cast-iron casserole, combine the beans with the carrot, celery, whole onion and bacon. Wrap the cloves, thyme and peppercorns in a large square of cheesecloth, tie with kitchen string and add to the casserole along with the water. Bring to a boil, then cover partially and simmer over moderate heat until the beans are tender, about 1 hour. Add the sausages during the last 10 minutes of cooking.
Drain the beans in a colander set over a bowl; reserve 3 cups of the cooking liquid. Discard the carrot, celery, onion and the cheesecloth bundle. Transfer the bacon to a cutting board and cut into 1/2-inch pieces. Slice the sausages diagonally 3/4 inch thick. Add the bacon and sausages to the beans.
Preheat the oven to 400°. Wipe out the casserole and melt 3 tablespoons of the butter in it. Add the chopped onion, garlic and bay leaves, cover and cook over moderate heat, stirring occasionally, until the onion is softened but not browned, about 6 minutes. Add the rice and stir to coat with the butter. Add the reserved 3 cups of cooking liquid and bring to a boil. Cover and cook over moderately low heat until the rice is just tender, about 15 minutes; the rice should be a little soupy. Stir in the heavy cream and the beans and season with salt and white pepper. Discard the bay leaves.
Butter a shallow 3-quart baking dish. Spoon the rice and beans into the dish and smooth the top. In a small bowl, toss the panko with the 4 tablespoons of melted butter so the crumbs are evenly moistened. Sprinkle the panko over the rice and beans. Bake for about 15 minutes, or until heated through.
Preheat the broiler. Broil the dish for about 2 minutes, shifting the dish once or twice, until the crumbs are evenly golden and crisp. Serve right away.