Grease a baking dish and spread the bread cubes evenly inside.
Whisk together eggs, milk, brown sugar, vanilla, cinnamon, nutmeg, and salt until smooth. Pour this mixture evenly over the bread, ensuring all pieces are coated.
Cover and refrigerate overnight, or let it sit at room temperature for a while so the bread absorbs the liquid.
Preheat the oven and prepare the topping by combining melted butter, brown sugar, and pecans.
Drizzle the topping evenly over the soaked bread mixture.
Cover and bake until the casserole begins to set, then uncover and continue baking until the top is golden brown and slightly crisp.
Remove from the oven and let it rest briefly before serving with maple syrup.