Preheat your oven to 350°F (175°C).
In a large mixing bowl, whisk together the eggs, milk, granulated sugar, vanilla extract, ground cinnamon, and salt until well combined.
Place the cubed brioche bread in a greased 9x13 inch baking dish. Pour the egg mixture over the bread, ensuring all pieces are soaked.
Cover the baking dish with plastic wrap and refrigerate for at least 30 minutes, or overnight for best results.
Once ready, remove the plastic wrap and bake the casserole in the preheated oven for 45 minutes, or until the top is golden brown and the custard is set.
Allow to cool slightly before cutting into squares. Serve warm with maple syrup and a dusting of powdered sugar if desired.
For added flavor, you can mix in berries, chocolate chips, or nuts before baking.
If you prefer a crispier texture, broil the casserole for the last 2-3 minutes of baking.