01 - Preheat oven to 350°F. Generously butter a 9x13-inch baking dish to prevent sticking.
02 - Distribute bread cubes evenly in the prepared baking dish. Sprinkle raisins over the bread if using.
03 - Whisk together milk, heavy cream, eggs, sugar, melted butter, vanilla, cinnamon, nutmeg, and salt in a large bowl until fully combined.
04 - Pour custard mixture over bread cubes. Press down gently to submerge bread. Allow to rest for 10 minutes so bread absorbs liquid.
05 - Bake for 40 to 45 minutes until golden brown and set, with a slight jiggle in the center.
06 - While pudding bakes, melt butter in a small saucepan over medium heat. Whisk in flour and cook 1 to 2 minutes until bubbly but not browned.
07 - Gradually whisk in milk and cream. Add sugar and salt. Cook while stirring constantly for 5 minutes until thickened.
08 - Whisk egg yolk in a small bowl. Add 2 to 3 spoonfuls of hot sauce while whisking quickly to temper the yolk, then return mixture to saucepan.
09 - Remove from heat. Stir in vanilla extract. Keep warm until ready to serve.
10 - Slice warm bread pudding into portions and drizzle with vanilla sauce immediately before serving.