Cook the pasta in a large pot of boiling salted water until al dente.

Using a mortar and pestle, mash the salt and garlic cloves together into a paste. Warm the yogurt slightly in a saucepan. Remove a small amount of warmed yogurt from the pan, and stir together with the garlic paste. Stir this mixture into the remaining yogurt.

Drain the pasta, and rinse in cold water. Place in a casserole or deep serving dish, toss with 1 tablespoon butter or margarine. Toss with half of the garlic-yogurt sauce. Spread the remaining sauce over the pasta. Garnish with the parsley.