The night before: Slice the bread into 20 slices, 1-inch each. Arrange the slices in a generously buttered 9 by 13-inch flat baking dish in 2 rows, overlapping the slices.
In a large bowl, combine the eggs, milk, cream, granulated sugar, vanilla, cinnamon, and salt and beat with a rotary beater or whisk until blended but not too bubbly. Pour mixture over the bread slices, making sure all are covered evenly with the milk-egg mixture. Spoon some of the mixture in between the slices. Cover with foil and refrigerate overnight.
The next day: Preheat oven to 350 degrees F.
Combine the flour, brown sugar, cinnamon, salt, and nutmeg in a medium bowl. Cut in the butter pieces with a pastry blender until mixture is crumbly. Sprinkle the topping over the bread mixture, distributed evenly.
Bake for 45 minutes, until puffed and lightly golden. Serve with maple syrup.
