Spray a 9x13 baking dish with cooking spray. Place the cubed bread into the baking dish, and set aside.
Place the eggs, milk, heavy cream, sugar, brown sugar, vanilla, cinnamon, and salt into a large bowl. Whisk together until well combined. Some of the cinnamon may float on top, but that's okay.
Pour the custard over the bread cubes. Take a large spoon and press the bread into the custard so it starts to soak it up. Cover the dish and place it in the fridge to soak for at least 6 hours, or overnight.
Preheat the oven to 350°F.
In a small bowl, whisk together the melted butter, brown sugar, and cinnamon until smooth. Drizzle this mixture all over the top of the casserole.
Cover with aluminum foil and bake for 30 minutes. Remove the tin foil and bake for another 25-30 minutes until the top is golden brown and a knife inserted into the center comes out clean.
Let cool for 15 minutes. Slice and serve with a dusting of powdered sugar and a drizzle of maple syrup. Feel free to add more of your favorite toppings, too.
