Prep your pan and oven: Heat the oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter.
Dry out the bread (if needed): If your bread is fresh, spread the cubes on a sheet pan and toast for 8–10 minutes. You want them slightly dry so they soak up the custard without getting mushy.
Whisk the custard: In a large bowl, whisk pumpkin puree, eggs, milk, cream, maple syrup, vanilla, spices, and salt until smooth.
The mixture should be pourable and even in color.
Combine: Add the bread cubes to the bowl and toss gently to coat. Let it sit for 10 minutes so the bread absorbs the custard. If using nuts or cranberries, fold them in now.
Assemble: Pour everything into the prepared baking dish.
Press down lightly so all pieces touch the custard. Drizzle the top with melted butter for extra color and flavor.
Bake: Bake uncovered for 40–50 minutes. The center should be set but still tender, and the top should be golden.
If it browns too quickly, tent with foil for the last 10 minutes.
Rest and serve: Let it rest for 10 minutes before cutting. Serve warm with a little maple syrup, a dusting of powdered sugar, or a spoonful of Greek yogurt.
Make-ahead option: Assemble the casserole the night before, cover, and refrigerate. Bake the next morning, adding 5–10 extra minutes since it will be cold going into the oven.