Topping:
Coat a 9x13-inch deep-dish baking dish with butter. In a large bowl, add the brioche and chopped apples, then sprinkle with cinnamon and apple pie seasoning, tossing to coat the bread and apples evenly. Place in a prepared baking dish and set aside. For the custard, whisk eggs, milk, cream, brown sugar, and vanilla until smooth, then pour evenly over the bread and apple mixture, pressing down gently to coat the bread and arrange the apple pieces evenly throughout. Cover with cling wrap and refrigerate for at least 4 hours or overnight. For topping, mix melted butter, brown sugar, cinnamon, salt, and flour together until small pieces form. Add extra flour, 1 TBLS at a time, until the mixture is pea-sized and crumbly. Refrigerate in a covered bowl until you are ready to bake the casserole. Preheat the oven to 350°F, sprinkle the topping over the casserole, and bake for 45 to 50 minutes, or until golden and set. Drizzle with maple syrup (optional) before serving warm.