In a small heavy saucepan, melt butter with brown sugar and corn syrup over moderate heat, stirring until smooth and melted completely together. Pour mixture into a 9x13x2-inch baking dish coated with non-stick spray. Sprinkle pecans over melted mixture. Place cut slices of French baguette bread on top of melted mixture-press down lightly with hands to ensure bread soaks up melted mixture.
In a bowl, whisk together eggs, half and half, vanilla, Grand Marnier or orange juice and salt until well combined. Pour mixture evenly over top of bread and melted mixture. Chill bread mixture, covered, overnight (at least 8 hours and up to 1 day)
Preheat over to 350 degrees and bring bread mixture to room temperature.
Bake bread mixture, uncovered, in middle of oven until puffed and edges are pale golden, 40 to 45 minutes. Keep an eye on it so you don't burn it.
Serves 4 to 8-depending on size of serving.