Preheat oven to 325 degrees.
Cut the brioche loaf into 1 inch dice. Place in a 2 quart baking dish. Drizzle with melted butter. Toss chunked white chocolate with bread cubes.
Combine milk, cream, sugar, and vanilla bean and bring to a boil over medium heat until sugar is disolved. Whisk eggs until smooth. Add hot milk mixture to eggs slowly, stirring contsantly. Do not wisk or custard will have a great deal of foam on the surface. Skim foam from custard. Strain custard over bread and chocolate. Let stand for 10 minutes to allow custard to soak into bread.
Place baking dish in another larger pan. Pour hot water into larger dish to reach 1 inch up side of dish. Bake the bread pudding for about 45 minutes to 1 hour, until custard is set and brioche is golden.