Grease a 9x13-inch ceramic or glass baking dish generously with softened butter. Arrange the 1-inch brioche bread cubes evenly across the dish, gently pressing them into a uniform, level layer.

In a large glass bowl, whisk together the 8 eggs, whole milk, heavy cream, 1/3 cup maple syrup, pure vanilla extract, ground cinnamon, nutmeg, and sea salt until completely smooth, frothy, and pale yellow.

Pour the velvety custard slowly and evenly over all the brioche cubes, ensuring every single piece is thoroughly moistened. Press down lightly with the back of a spatula so the bread absorbs the liquid.

Cover the dish tightly with aluminum foil or plastic wrap. Transfer to the refrigerator to chill for at least 4 hours, or ideally overnight (8 to 12 hours) so the custard permeates to the very core of the brioche.

When ready to bake, remove the dish from the refrigerator and let it sit at room temperature for 25 to 30 minutes while preheating your oven to 350°F (175°C).

In a medium bowl, combine the chopped pecans, packed brown sugar, melted butter, 2 tablespoons maple syrup, cinnamon, and flaky sea salt. Stir with a fork until the pecans are glossy and coated in clumpy streusel.

Scatter the candied pecan streusel evenly across the top of the soaked brioche bake.

Bake uncovered at 350°F (175°C) for 40 to 45 minutes. The center should be set (no liquid custard when pierced with a knife), the brioche cubes puffed and pillow-soft, and the pecan topping deeply caramelized, fragrant, and shatteringly crisp.

Remove from the oven and let rest for 10 minutes to allow the custard to settle for clean, beautiful slicing.

Dust the golden top generously with powdered sugar. Slice into hearty squares and serve warm with cascades of pure maple syrup, fresh berries, and a pat of salted butter!