In a big mixing bowl, combine eggs, milk, granulated sugar, cinnamon, nutmeg, vanilla, and salt. Give it a good whisk until everything is mixed together.
Take a slice of brioche bread and spread just under a tablespoon of butter on top. Sprinkle a couple of teaspoons of brown sugar over it, enough to cover the slice. Repeat this with the rest of the bread slices. Arrange them in a round baking dish.
Pour the egg mixture over the bread slices.
Cover the dish and let it chill in the refrigerator for 2-3 hours or overnight.
Bake it at 350 degrees Fahrenheit for 35-40 minutes or until the top turns a beautiful golden brown.
Once out of the oven, sprinkle some powdered sugar on top and/or drizzle with maple syrup.