Butter a 9-by-13-inch baking dish. Spread half of bread in dish, overlapping. Scatter white chocolate chips and 1 cup of cranberries over. Layer remaining bread and cranberries.
In a large pan, warm milk, cream and sugar over medium heat, stirring until mixture just comes to a boil. Remove from heat, add chopped chocolate; let stand 10 minutes. Stir until smooth.
In a bowl, whisk eggs, yolks and vanilla. Gradually whisk in cream mixture. Pour over bread; press bread down. Cover; refrigerate for at least 2 and up to 24 hours, pressing bread down occasionally.
Preheat oven to 350ºF. Line a large baking sheet with foil. Place baking dish on sheet, remove plastic wrap and cover with foil. Bake for 45 minutes. Remove foil and bake 30 to 40 minutes longer, until golden and puffed. Let stand 20 minutes before serving.