Preheat oven to 350°F (175°C) and grease a 9×13-inch baking dish. Spread cubed bread evenly in the dish.
Whisk eggs, milk, cream, brown sugar, melted butter, vanilla or bourbon, cinnamon, nutmeg, and salt until smooth.
Pour custard over bread and gently press to soak. Let rest for 15 minutes.
Mix pecans, brown sugar, melted butter, heavy cream, and vanilla in a bowl.
Spoon pecan topping evenly over bread. Bake uncovered for 40–45 minutes until golden and set. Cover loosely if browning too quickly.
Let rest for 10 minutes before serving warm.