Combine syrup, butter, and sugar in a small saucepan. Simmer until the sugars have melted and it takes on a syrupy consistency.
Spray a 13" x 9" pan with cooking spray. Place one layer of bread in the dish.
Pour the syrup mixture over the bread.
Place another layer of bread over the syrup mixture.
Beat eggs, milk, vanilla, and salt in a bowl. Pour evenly over the bread.
Cover and refrigerate overnight.
Preheat oven to 350°.
Bring the casserole to room temperature.
Bake uncovered for 45 minutes at 350°.
Dust with powdered sugar prior to serving. Serve with jams, syrup, and more powdered sugar.