Combine 1 1/2 cups cooked rice, 1 1/2 cups milk, 1/4 c sugar and 1/4 tspsalt. Cook over medium heat until thick and creamy, 15 to 20 minutes. Stir in beaten egg and optional raisins. Cook 2 minutes more, stirring constantly. Remove from heat, and stir in butter and vanilla. Serve warm.