Combine rice and 2 cups milk, sugar and salt in a heavy saucepan. Cook over medium heat and stir occasionally until thick and creamy, 15-20 minutes. Blend remaining milk and egg (make sure egg is beaten well) and stir into rice mixture. Add sultanas and cook two minutes longer, stirring occasionally. Add butter and vanilla. Spoon into serving dishes and sprinkle with nutmeg and/or cinnamon.