The day before, make the sauce. In a sauce pan, combine the butter, brown sugar, and orange juice, and bring to a boil, stirring frequently. Set aside to thicken for about ten minutes, then stir.
In a bowl, combine the eggs, milk, vanilla, and cinnamon. Mix together.
Grease a 9x13” glass baking dish and coat the bottom with sauce.
Dip bread slices in the custard mixture and place them in the pan on top of the sauce. Pour additional sauce on top of the layer of bread slices, reserving some for serving.
Refrigerate overnight.
In the morning, pre-heat the oven to 350 degrees. Bake the french toast for about 50 minutes until golden brown. Serve with reserved sauce.