1. Preheat the oven to 350°F (175°C) and grease a baking dish.
2. In a large bowl, whisk together the milk, sugar, eggs, melted butter, vanilla extract, and cinnamon.
3. Add the cubed bread to the mixture, stirring gently to coat. Let it soak for 10-15 minutes.
4. Stir in raisins, if using.
5. Pour the mixture into the prepared baking dish and spread it evenly.
6. Bake for 40-45 minutes, or until the top is golden and the center is set.
7. Allow the bread pudding to cool slightly before serving.

For Vanilla Bean Sauce:

1. In a saucepan, combine the cream, milk, and sugar over medium heat, stirring until the sugar dissolves.
2. Scrape the seeds from the vanilla bean and add them to the mixture (or use vanilla extract).
3. Add the butter and stir until melted.
4. In a separate bowl, whisk the egg yolk, then slowly pour in a little of the hot cream mixture, whisking constantly to temper the egg.
5. Slowly add the tempered egg mixture back into the saucepan, stirring constantly, and cook for another 2-3 minutes until slightly thickened.
6. Remove from heat and let the sauce cool slightly before drizzling over the bread pudding.