Prepare the Bread: Cut your bread into 1-inch cubes and let them sit out overnight to dry slightly.
Mix the Custard: In a large bowl, whisk together eggs, milk, cream, sugars, vanilla extract, cinnamon, nutmeg, and salt.
Combine Bread and Custard: Place the bread cubes in the baking dish and pour the custard mixture evenly over them. Press lightly to ensure every piece is soaked.
Chill: Cover with foil and refrigerate for at least 2 hours or overnight.
Preheat the Oven: Set your oven to 350°F (175°C).
Bake: Bake covered for 30 minutes. Remove the foil and bake for an additional 25-30 minutes, or until the top is golden and crispy.
Serve: Let the casserole cool for 5 minutes before serving. Top with your favorite toppings.