Grease a baking dish with butter or baking spray. Add the cubed bread pieces to the pan, then top with chocolate chunks and frozen blueberries.
In a large mixing bowl, combine large eggs, heavy cream, whole milk, brown sugar, granulated sugar, maple syrup, pure vanilla extract, orange zest, ground cinnamon, and kosher salt. Whisk well.
Pour the custard mixture over the bread, then use a spatula to gently submerge everything as best you can. Wrap tightly with plastic wrap or aluminum foil, then refrigerate.
Place on a sheet pan and bake. Check at 40 minutes and if the top is browning too quickly, cover with aluminum foil before returning to the oven. Allow the French toast casserole to cool before slicing. Dust with powdered sugar.
In a large mixing bowl, combine heavy cream, vanilla extract, powdered sugar, and ground cinnamon. Use a hand mixer (or stand mixer) to whip on medium speed until soft peaks form.
Cut the casserole into slices, then serve with a dollop of cinnamon whipped cream and a bit of fresh fruit on the side. Enjoy!