Cube and dry the brioche: Cut the brioche loaf into uniform 1-inch cubes. If the bread is very fresh, spread cubes on a baking sheet and bake at 300°F (150°C) for 10 minutes to lightly dry them out so they absorb maximum custard without becoming mushy.

Arrange in baking dish: Grease a 9x13-inch ceramic baking dish with butter. Transfer the brioche cubes into the dish, spreading them evenly to the edges.

Whisk the spiced pumpkin custard: In a large mixing bowl, whisk together the eggs, whole milk, heavy cream, pumpkin puree, maple syrup, vanilla paste, cinnamon, pumpkin pie spice, and sea salt until smooth, velvety, and fully blended.

Pour and soak (Overnight Secret): Slowly pour the pumpkin custard evenly over the brioche cubes, pressing down gently with a spatula so every piece is submerged. Cover tightly with plastic wrap and refrigerate for at least 4 hours, or ideally overnight (8 to 12 hours) so the custard permeates every bread fiber.

Mix the crunchy pecan streusel: In a small bowl, combine flour, dark brown sugar, cinnamon, and cold cubed butter. Use your fingers or a pastry cutter to work the butter until pea-sized crumbles form, then stir in the chopped pecans.

Bake to puffed golden perfection: Preheat your oven to 350°F (175°C). Uncover the baking dish and sprinkle the pecan streusel evenly across the top. Bake for 45 to 50 minutes until the casserole is puffed, the center is set with a slight gentle jiggle, and the streusel is crisp and deep mahogany golden.

Rest, dust & serve: Let cool for 10 minutes to set cleanly. Dust with powdered sugar, top with whipped salted butter, drizzle generously with warm amber maple syrup, and serve warm!