Grease a 9x13-inch ceramic or glass baking dish with butter. Place cubed brioche bread evenly into the dish.

In a large bowl, whisk together eggs, whole milk, heavy cream, pumpkin puree, brown sugar, vanilla extract, cinnamon, nutmeg, ginger, and salt until smooth.

Pour the pumpkin custard evenly over the brioche cubes. Press down lightly with a spatula so all bread pieces are submerged. Cover and chill in refrigerator for at least 2 hours or overnight.

In a small bowl, prepare the streusel by combining flour, brown sugar, and cinnamon. Cut in cold butter with a fork until crumbly, then stir in chopped pecans.

Preheat oven to 350°F (175°C). Uncover the chilled casserole and scatter the pecan streusel evenly across the top.

Bake for 40 to 45 minutes until puffed, golden, and center is set. Cool for 10 minutes, drizzle with maple syrup, and serve warm.