Combine rice and 1 1/2 cups milk, sugar and salt in heavy saucepan. Cook over medium heat stirring occasionally until thick and creamy, 15 to 20 minutes.
Blend remaining half cup milk and egg. Stir into rice mixture. Add raisins. Cook 2 minutes longer, stirring occasionally.
Add butter and vanilla.
Spoon into serving dishes. Sprinkle with nutmeg or cinnamon if desired.