Make vanilla sugar one week in advance by slicing vanilla bean in half and scraping seeds into sugar. Leave bean buried in the middle.
Preheat oven to 425.
Cut bread into 1" slices and generously butter one side. Mix eggs, milk and vanilla with a blender. Pour custard over bread and let sit one hour on the countertop, or overnight in the fridge. Place slices on a cookie sheet lined with wax paper and sprinkle each one with vanilla sugar. Bake for 20-25 minutes, or until golden brown. Serve with honey or maple syrup.