Butter a 2 quart soufflé dish or 6 x 10 inch baking dish. Dust with bread crumbs. Set aside. Remove crusts from bread and cut bread into cubes. Set aside. In skillet, sauté mushrooms and onions in Madeira over medium heat. Stir in crabmeat.
In prepared soufflé dish alternate layers of bread cubes and crab mixture, ending with bread cubes. In food processor or blender, whirl milk, eggs, cheese, salt, mustard and pepper til thoroughly blended. Slowly pour this mixture over bread cubes. Cover and refrigerate overnight.
Bake uncovered at 325 for 1 hour, 30 minutes if using soufflé dish or 1 hour if using 6 x 10 inch baking dish. Strata is done when knife inserted just off center comes out clean. Serves 6 to 8