Preheat oven to 375° F. Place butter in 13x9x2-inch baking pan. Place pan in oven for 5 to 6 minutes or until butter melts.
Stir in brown sugar; spread brown sugar mixture evenly in dish. Set aside. Arrange bread slices on large baking sheet. Place in oven for 5 minutes to dry.
In large bowl, whisk together eggs, half & half and vanilla. Dip both sides of each bread slice in egg mixture. Arrange slices in baking pan on top of brown sugar mixture, overlapping as necessary.
Pour any remaining egg mixture over slices. Sprinkle with cinnamon.
Bake, uncovered, 25 to 30 minutes or until golden brown. Let stand 10 minutes before serving. Sprinkle with powdered sugar to serve.