Spray a 9x3 inch baking dish with nonstick spray.
Layer the bread slices in the dish.
In a large bowl, whisk together the eggs and the milk.
Whisk in the brown sugar and melted butter, then whisk in the vanilla, cinnamon, and salt.
Pour the custard all over the bread in the dish, making sure each slice of bread is covered.
Cover the dish and refrigerate overnight.
Remove the dish from the fridge about 30 minutes before baking the next morning. Preheat the oven to 350 degrees Fahrenheit.
Bake the French toast for 45 minutes, or until puffed, crispy, and golden. Remove it from the oven and sprinkle with powdered sugar. Serve with fresh fruit, whipped cream, and maple syrup!