Preheat oven to 400 degrees F.
Butter baking dish and set aside. In a small bowl, combine butter, 1/4 cup sugar, cinnamon
and salt. Generously butter both sides of brioche
bread with butter mixture. Toast on a baking sheet in the oven 5 to 10 minutes, or until bread turns golden brown. Cut toast on a diagonal into triangles and arrange in the prepared baking dish. In a medium bowl, whisk
together eggs, heavy cream
, orange juice, salt, remaining sugar, and vanilla. Stir in grapes and pour over bread slices in baking dish. Let rest 10 minutes for bread to absorb some of the egg mixture, gently pressing down a few times to help absorb. Bake 25 to 30 minutes until crust
is golden and crispy in parts and custard
is set. Remove from the oven, dust
with powdered sugar, drizzle
with maple syrup and serve.