Melt the butter in a saucepan over medium heat. Stir in brown sugar and corn syrup until smooth.
Pour the mixture into a greased 9x13-inch baking dish.
Arrange bread slices over the sugar mixture in a single layer.
In a separate bowl, whisk together eggs, milk, vanilla, and salt. Pour evenly over the bread.
Cover and refrigerate overnight.
In the morning, preheat oven to 350°F (175°C).
Bake uncovered for 35–40 minutes, or until golden and bubbly.
Serve warm, optionally topped with powdered sugar or fresh berries.