Cut bread into small, 1-inch cubes and spread the pieces evenly in a large baking sheet and just let them dry for about 24 hours.
Preheat oven to 200°. Cut the bread the same way as you would be making is ahead of time.
Spread bread cubes on a large rimmed baking sheet and place it into the oven.
For French Toast Casserole and Bread Puddings, bake it for 45 minutes – 1 hour, that way it’s not completely dry.
French Toast Casserole:
Preheat the oven to 350° and grease a casserole dish. You can use a 9×13 casserole dish or a deep 9×9 casserole dish.
Spread stale bread in the baking dish evenly.
In a large bowl, whisk together eggs, milk, heavy whipping cream, vanilla extract, sugar, and cinnamon. Whisk until all smooth and combined evenly.
Pour egg mixture over the Brioche bread cubes evenly, all over. Press down all over the bread so that it all gets soaked.
Bake for 45-50 minutes in a 9×13 casserole dish, or 50-55 in a 9×9 casserole dish. TIP: If the top is browning too fast, you can cover the top loosely with a sheet of aluminum foil when it starts to brown.
Sweet Butter Syrup:
Melt butter in a small sauce pot over medium heat.
Add powdered sugar, heavy whipping cream, cinnamon, and nutmeg and stir until combined.
Bring to simmer and simmer for a couple of minutes but keep an eye on it. Take off heat and stir in vanilla extract.
Once French Toast Casserole is baked, pour prepared syrup all over the top and give it a few minutes to soak through. (Or, you can top off each individual slice of casserole with syrup instead.)