01 - Preheat your oven to 350°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - Place the bread cubes in the prepared dish. Sprinkle raisins evenly over the bread if using.
03 - In a large bowl, whisk together the milk, cream, eggs, sugar, melted butter, vanilla extract, cinnamon, nutmeg, and salt until fully combined.
04 - Pour the custard mixture evenly over the bread cubes. Press down gently to ensure the bread absorbs the liquid. Let sit for 10 minutes.
05 - Bake for 40 to 45 minutes, until the pudding is golden and set but still slightly soft in the center.
06 - While the pudding bakes, prepare the vanilla sauce. In a small saucepan, melt butter over medium heat. Stir in the flour and cook for 1 to 2 minutes until bubbling but not browned.
07 - Gradually whisk in the milk and cream, ensuring no lumps form. Add sugar and a pinch of salt. Cook, stirring constantly, until thickened, about 5 minutes.
08 - In a small bowl, whisk the egg yolk. Slowly add a few spoonfuls of the hot sauce to the yolk to temper, then pour back into the saucepan, whisking constantly.
09 - Remove from heat and stir in the vanilla extract. Keep warm until serving.
10 - Serve the warm bread pudding topped with the warm vanilla sauce.