Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish.
Spread the bread cubes evenly in the prepared baking dish.
Whisk together pumpkin puree, milk, heavy cream, eggs, brown sugar, granulated sugar, vanilla, pumpkin pie spice, cinnamon, nutmeg, salt, and melted butter.
Pour the pumpkin custard evenly over the bread cubes.
Gently press the bread into the custard and let it soak for 10–15 minutes.
Sprinkle chopped pecans over the top if using.
Bake for 45–50 minutes until the center is set and the top is lightly golden.
For the vanilla sauce, melt the butter in a saucepan over medium heat.
Stir in heavy cream, sugar, vanilla, and salt until smooth and slightly thickened.
Serve the warm bread pudding drizzled generously with the vanilla sauce.