Preheat the oven to 400°. Butter a 2-quart soufflé dish. Cook the carrots in boiling salted water until tender, about 30 minutes; drain well. Puree the carrots in a food processor, then scrape into a bowl. Let cool slightly, then stir the egg yolks, 1/4 cup of the Parmesan, the butter, flour, salt, pepper and a few gratings of nutmeg into the carrot puree.