Preheat oven to 400 degrees. In a large bowl, combine cauliflower, heavy cream, flour, and 3/4 cup grated Parmesan. Season with salt and pepper and toss to combine. Transfer mixture to a 2-quart baking dish, cover tightly with foil, and bake 30 minutes. In a small bowl, combine 1/4 cup grated Parmesan and breadcrumbs. Sprinkle over cauliflower. Dot with butter and bake, uncovered, until topping is golden brown and cauliflower is tender when pierced with a knife, 10 to 15 minutes. Let cool 5 minutes before serving.