Heat oven to 375 degrees and position an oven rack in upper third of oven. Use 1 tablespoon butter to butter a 9-inch round or square baking pan.
In a blender, purée cottage cheese, milk, mustard, cayenne, nutmeg and salt and pepper together. Reserve ¼ cup grated cheese for topping. In a large bowl, combine remaining grated cheese, milk mixture and uncooked pasta. Pour into prepared pan, cover tightly with foil and bake 30 minutes.
Uncover pan, stir gently, sprinkle with reserved cheese and dot with remaining tablespoon butter. Bake, uncovered, 30 minutes more, until browned. Let cool at least 15 minutes before serving.