Preparation: Rinse the rice under cold water until the water runs clear. Soak the rice in water for 15-30 minutes. Drain and set aside.
Cooking: In a large pot, combine the milk and cinnamon stick. Bring to a boil over medium heat, then add the rice. Reduce heat to low and simmer, stirring frequently, until the rice is tender and the mixture begins to thicken, about 20-25 minutes.
Sweetening: Stir in the sugar and raisins (if using). Continue to simmer for another 10 minutes, stirring occasionally, until the mixture is creamy.
Finishing: Remove from heat and stir in vanilla extract. Discard the cinnamon stick. Let cool slightly before serving.
Serving: Serve warm or chilled, sprinkled with ground cinnamon on top.