Preheat oven to 350°. Butter bread on both sides. In large bowl, whisk together remaining ingredients. Place a layer of buttered bread in bottom of 9"x5" loaf pan. Continue layering until bread is 1 inch from top. Pour liquid mixture over bread slowly, allowing it to absorb. Stop when bread is soaked. Place pan in center of deep oven proof pan. Pour boiling water around it until water is halfway up loaf pan. Place in center oven rack and back until set, about 45 minutes.
Remove pudding from oven and cool slightly. To serve, place thick slice on a plate and top with hot or cold caramel sauce.