Preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish.

In a large bowl, whisk together the heavy cream, whole milk, eggs, brown sugar, melted butter, vanilla, cinnamon, nutmeg, and salt until smooth.

Add the cubed bread to the mixture and press gently so the bread soaks up the custard; wait about 10–15 minutes until the bread looks plump.

Give the mixture one last stir to distribute evenly.

Pour the soaked bread mixture into your greased dish, spreading it so the top is even.

Bake for about 40 minutes, or until the edges are golden and the center feels set but slightly jiggly — a toothpick should come out mostly clean.

While the pudding is baking, combine heavy cream, brown sugar, and butter in a saucepan over medium heat.

Stir until the sugar fully dissolves and the sauce begins to thicken and shine.

Remove from heat and stir in the bourbon and vanilla; the aroma will bloom.

Serve the pudding warm, spoon the bourbon vanilla sauce over each slice, and add a scoop of vanilla ice cream if desired.