In a small heavy saucepan melt butter with brown sugar
and corn syrup over moderate heat, stirring, until
smooth and pour into a 13- by 9- by 2-inch baking
Cut six 1-inch thick slices from center portion
of bread, reserving ends for another use, and trim
crusts. 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 1 day.
Preheat oven to 350° F. and bring bread to room
temperature. Bake bread mixture, uncovered, in middle of oven until puffed and edges are pale golden, 35 to 40 minutes. Serve hot French toast immediately.