Preheat your oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish with butter or cooking spray.

Cut the day-old bread into 1-inch cubes and scatter the cubes evenly in the prepared baking dish.

In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, granulated sugar, vanilla extract, ground cinnamon, and nutmeg until smooth.

Pour the custard over the bread cubes and let it rest for 10 minutes.

Cover with aluminum foil and bake for 30 minutes, then remove the foil and bake for another 15 minutes until golden brown.

In a medium saucepan over medium heat, combine granulated sugar and water, stirring until it turns amber. Carefully whisk in warm heavy cream, butter, vanilla extract, and salt.

Cut into squares and plate each serving, drizzling the warm caramel sauce on top.