In a small heavy saucepan melt butter with brown sugar and corn syrup over moderate heat, stirring until smooth and pour into a 13"x9"x2" baking dish. Cut six 1-inch thick slices from center portion of bread, reversing ends for another use. Arrange bread slices in one layer in baking dish, squeezing them slightly to fit.

In a bowl whisk together eggs, half-and-half, vanilla, Grand Marnier and salt until combined well and pour evenly over bread. Chill bread mixture, covered, at least 8 hours and up to 24 hours.

Preheat oven to 350° and bring bread to room temperature. Bake uncovered in middle of oven until puffed and golden, 35 to 40 minutes. Serve immediately.