1Preheat the oven to 350 degrees. Place 4 T of the butter in a 13x9" baking dish and place in the oven to melt.
2Meanwhile, combine the bread cubes, buttermilk and raisins in a large mixing bowl. In a separate bowl, whisk together the eggs, brown sugar, vanilla extract and rum extract. Pour over the bread mixture and stir gently to combine.
3Transfer to the prepared pan nd pour over the melted butter. Bake 1 hour.
4Meanwhile, combine the remaining butter, granulated sugar, egg yolk and water in a small saucepan. Stir well and place over medium heat. Stir constantly until the sugar dissolves and the sauce begins to thicken about 10 min. Add the rum.
To serve, cut the warm bread pudding in squares, drizzle with the sauce and serve warm.