Day-old brioche works best for soaking up the custard mixture in this hybrid dessert. The sweet-tart apples are a nice counterpoint to the rich pudding.
Preheat oven to 350 degrees with rack set in the lower third of the oven. Lightly butter a 9-inch pie plate; set aside.
In a large bowl, whisk together cream, milk, and eggs. Add brioche and gently toss to coat. Set aside at room temperature for 30 minutes to soak.
Meanwhile, melt butter in a medium saucepan over medium heat. Remove from heat and add granulated sugar, brown sugar, vanilla, spices, and salt; stir until smooth and well combined. Add apples and toss to coat.
Gently fold apple mixture into the bread mixture until well combined. Spoon bread and apple mixture into prepared pie plate, then pour remaining liquid over top just to fill to the edge of the dish (you may not use all of it). Sprinkle with turbinado sugar, if desired.
Bake, covered with parchment-lined foil, for 45 minutes (with a parchment-lined baking sheet placed at the bottom of the oven to catch drips). Uncover and continue to bake until bread pudding is golden brown and set in the center, 30 to 35 minutes more. Let sit on a wire rack 10 to 20 minutes before serving with ice cream. Bread pudding is best served warm, but can be kept refrigerated, tightly covered, up to 3 days.
