Prepare the Brioche Bread: Cut the brioche loaf into 1-inch cubes. If fresh, spread the cubes across a large baking sheet and toast at 325°F (165°C) for 10-12 minutes until dry to the touch but not deeply browned. This step prevents soggy casserole and ensures maximum custard absorption. Butter a 9x13-inch baking dish.

Caramelize the Apples: Melt 4 tablespoons unsalted butter in a large skillet over medium heat. Add sliced Honeycrisp apples, brown sugar, cinnamon, lemon juice, and a pinch of salt. Cook, tossing frequently with a wooden spoon, for 6 to 8 minutes until the apples are tender-crisp and coated in a glossy, bubbly cinnamon caramel glaze. Remove from heat and let cool slightly.

Whisk the Rich Custard: In a large mixing bowl, vigorously whisk together the 8 eggs, whole milk, heavy cream, pure maple syrup, vanilla extract, cinnamon, nutmeg, and fine salt until silky smooth and completely combined without egg streaks.

Layer and Soak: Place half of the toasted brioche cubes in the prepared baking dish. Spoon half of the warm caramelized apples and their pan caramel evenly over the bread. Scatter the remaining brioche cubes on top, followed by the remaining caramelized apples. Slowly pour the spiced custard evenly over the entire dish, pressing down gently with a spatula so every cube absorbs the custard. Let rest for 20 minutes (or cover and refrigerate overnight).

Bake to Golden Puffed Perfection: Preheat your oven to 350°F (175°C). Scatter the chopped pecans and turbinado coarse sugar over the top, then drizzle with 2 tablespoons melted butter. Bake uncovered on the middle oven rack for 38 to 42 minutes, until the custard is set in the center, edges are caramelized and crisp, and the casserole is lightly puffed.

Rest, Dust, and Serve: Allow the French toast bake to cool for 8 to 10 minutes (it will settle gently while remaining piping hot inside). Dust generously with powdered confectioners sugar, slice into squares, and serve with warm amber maple syrup!