The night before: In a small saucepan over medium heat, melt the butter and brown sugar until bubbly and smooth, about 4 minutes. Pour the melted butter mixture at the bottom of a 9x13 casserole dish and spread evenly with a spatula.
In a large bowl whisk the eggs for 1 minute. Next add the half and half, vanilla, maple syrup, Grand Marnier (if using), and salt. Whisk until combined. Set aside.
Slice the bread into 1 inch slices. Arrange the slices in the casserole dish in a single layer over the brown sugar mixture, as many slices as you can fit. Depending on the size of the loaf you use, you may have leftover slices. Pour the custard mixture over the top of the bread slices. Cover with plastic wrap and chill overnight.
In the morning: When ready to bake, preheat the oven to 350 degree F. Bake uncovered for 40-45 minutes until lightly golden. Carefully remove the casserole dish from the oven, and flip each individual slice over with a spatula. Turn the oven onto broil, and broil on high until the sugar begins to brown and caramelize, about 2 minutes. Watch very carefully so that it doesn't burn! Top with fresh berries, cream, or maple syrup. Enjoy!