Spray a 9x13-inch baking dish with cooking spray. Arrange bread cubes evenly in the dish.
In a large bowl, whisk together eggs, pumpkin puree, milk, heavy cream, brown sugar, vanilla, pumpkin pie spice, cinnamon, salt, and nutmeg until smooth.
Pour pumpkin mixture evenly over bread cubes, pressing down gently to ensure all bread is soaked. Let sit for 10 minutes.
In a small bowl, toss pecans with melted butter and sprinkle over the top of the casserole.
Cover tightly with foil and refrigerate for at least 4 hours or overnight (or freeze at this point for up to 2 months).
When ready to bake, preheat oven to 350°F. Bake covered for 40 minutes, then uncover and bake for 10 more minutes until golden and puffed.
Let stand 10 minutes before serving. Serve warm with maple syrup, whipped cream, or a dusting of powdered sugar. If frozen, thaw overnight in refrigerator before baking.