Caramelize Apples: In a medium skillet over medium heat, melt 2 tablespoons of butter. Add the diced apples, brown sugar, cinnamon, and ¼ cup apple cider. Simmer for 5 to 6 minutes until the apples are lightly tender and glazed with reduced cider. Remove from heat and let cool slightly.

Arrange Bread: Grease a 9x13-inch ceramic baking dish with butter. Spread half of the cubed brioche bread across the bottom. Scatter the warm caramelized apples and their pan juices evenly over the bread, then top with the remaining brioche cubes.

Whisk Spiced Custard: In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, ½ cup apple cider, pure maple syrup, vanilla extract, cinnamon, nutmeg, and sea salt until completely smooth and emulsified.

Pour & Absorb: Pour the custard evenly over the brioche cubes in the baking dish, pressing down gently with a spatula so all bread pieces soak up the liquid. (Make-ahead tip: Cover tightly with foil and refrigerate overnight, or let soak for at least 20 minutes before baking.)

Make Streusel: In a small bowl, combine flour, brown sugar, and cinnamon. Cut in the cold butter with a pastry cutter or your fingertips until pea-sized crumbles form. Stir in the chopped pecans. Sprinkle the streusel generously over the top of the soaked casserole.

Bake to Golden Perfection: Preheat oven to 350°F (175°C). Bake covered with aluminum foil for 25 minutes. Remove the foil and continue baking uncovered for 20 to 25 minutes, until the top is deeply golden brown, the edges are puffed and crispy, and a knife inserted in the center comes out clean.

Rest, Dust & Serve: Let rest for 10 minutes before slicing. Dust with confectioners sugar, drizzle generously with warm maple syrup or boiled cider syrup, and serve warm with hot coffee.