1. Place beans in large bowl; cover with water. Soak 6 hours, or overnight. Drain.
2. Combine mushrooms in large bowl; cover with 7 cups boiling water, and soak 30 minutes. Drain, reserve soaking liquid, and chop mushrooms into 1/4-inch dice.
3. Heat 2 Tbs. oil in Dutch oven over medium heat. Add mushrooms, leeks, and carrots; sauté 5 to 7 minutes, or until beginning to brown. Stir in thyme and 1 Tbs. garlic; cook 30 seconds. Add drained beans, tomatoes, bay leaves, and reserved mushroom soaking liquid; cover; and bring to a boil. Reduce heat to medium-low, and simmer 1 1/2 to 2 hours, or until beans are tender and most of liquid is absorbed, adding more liquid if necessary. (Mixture should be a little soupy.) Add salt, and add pepper to taste; cook 5 to 10 minutes more. Let stand 30 minutes.
4. Heat remaining 3 Tbs. oil in skillet over medium heat. Add remaining 1 Tbs. garlic; warm 1 minute, or until garlic turns opaque. Remove from heat; stir in breadcrumbs.
5. Preheat oven to 350°F. Remove bay leaves from bean mixture, and spread breadcrumbs over top. Bake 30 minutes, or until breadcrumbs are golden brown.