Spray a 9x13-inch dish; spread bread evenly.
Whisk eggs, pumpkin, milk, cream, brown sugar, vanilla, spices, salt, and nutmeg smooth in a large bowl.
Pour evenly over bread; press gently to soak and rest 10 minutes.
Toss pecans with butter in a small bowl; sprinkle over casserole.
Cover tightly with foil; refrigerate at least 4 hours or overnight, or freeze up to 2 months.
Heat oven to 350°F; bake covered 40 minutes, then uncovered 10 minutes until golden and puffed.
Rest 10 minutes; serve warm with syrup, whipped cream, or powdered sugar. If frozen, thaw refrigerated overnight before baking.