Preheat oven to 325°F. In a saucepan, combine milk, rice, sugar and salt; bring to a boil over medium heat, stirring constantly. Pour into a greased 1-1/2-qt. baking dish.

Cover and bake for 45 minutes, stirring every 15 minutes. Add vanilla; cover and bake for 15 minutes longer. Remove from oven and let stand 15 -20 minutes to set up and thicken. Sprinkle with cinnamon if desired. Serve warm or chilled.