Cut the bread into 8 large wedges. Whisk the eggs, buttermilk, cream, granulated sugar, vanilla and cinnamon in a large baking dish. Add the bread and turn occasionally until soaked through, about 15 minutes. Preheat the oven to 250 degrees F.
Put the confectioners' sugar in a fine-mesh sieve. Melt 1 tablespoon butter in a large nonstick skillet over medium heat. Add half of the bread and dust generously with the confectioners' sugar; cook, turning and dusting often with more confectioners' sugar, until golden brown and caramelized, 10 to 12 minutes (add more butter to the skillet, if needed). Transfer the French toast to a baking sheet and keep warm in the oven. Add 1 more tablespoon butter to the skillet and repeat with the remaining bread. Serve with maple syrup.