Combine butter and brown sugar. Spread mixture on the bottom of a 13x9-inch greased baking dish. Place bread slices on top of brown sugar mixture. Combine eggs, milk, vanilla and cinnamon in a bowl. Pour over slices. Cover and refrigerate overnight. Preheat oven to 350. Bake, uncovered, 45 minutes. Sprinkle with powdered sugar and/or maple syrup. Serves 6-8.