Spray sides and bottom of 13x9-inch baking pan with cooking oil spray. In a small bowl, stir together sugar and butter. Spread mixture over baking pan evenly. Arrange bread slices on top of butter-sugar mixture.
In a large bowl, whisk together eggs, milk, vanilla, and cinnamon. Pour over bread. Cover with plastic
wrap and refrigerate for at least 3 hours or overnight.
Preheat oven to 350°. Let casserole sit at room temperature for 15 minutes.
Bake until lightly browned, about 25-30 minutes. With a spatula, turn over each slice and return to oven about 10-12 more minutes.
Top with confectioners’ sugar and serve with warm syrup, if desired.