Grease a 9x13-inch baking dish with melted butter.
Spread the bread cubes evenly in the dish.
In a large bowl, whisk together eggs, milk, cream, granulated sugar, brown sugar, vanilla, cinnamon, nutmeg, and salt until fully combined.
Pour the egg mixture evenly over the bread, making sure all pieces are soaked.
Gently press the bread down to absorb the custard.
Cover the dish with foil and refrigerate for at least 30 minutes or overnight for best results.
Preheat the oven to 350 degrees Fahrenheit.
Bake covered for 25 minutes, then uncover and bake for another 15 to 20 minutes until set and lightly golden on top.
Let rest for 5 minutes before serving.