Melt together in saucepan the butter, brown sugar maple syrup and rum extract (if using).
Butter/grease a 9 by 13 baking dish. Pour the mixture into the bottom of the pan.
Cut about 6 - 1/2 to 1 inch thick slices of the bread
Whisk egg, 1/2 & 1/2 , vanilla, grand mariner and salt. Pour evenly over the bread
COVER AND LET REST OVERNIGHT
Let mixture rest to room temperature in the morning.
Preheat oven to 350°
Bake @ 350° for 35 - 40 min.