Rinse the rice in a fine-mesh strainer under cool water until the water runs mostly clear. This removes excess surface starch and helps keep the finished pudding creamy rather than gummy.

Add the rinsed rice, water, cinnamon stick, and salt to a large heavy-bottomed saucepan. Bring to a boil over medium-high heat, then reduce the heat to low, cover, and cook until most of the water is absorbed and the rice is nearly tender, about 15 minutes.

Uncover the saucepan and stir in the whole milk and sweetened condensed milk. Bring the mixture just to a gentle simmer over medium-low heat; do not let it boil rapidly.

Cook uncovered, stirring frequently and scraping the bottom and corners of the pan, until the rice is fully tender and the pudding has thickened but is still a little loose, about 25 to 30 minutes. It will continue to thicken as it cools.

Remove the pan from the heat. Take out the cinnamon stick, then stir in the vanilla and raisins, if using. Let the pudding stand for 10 minutes before serving.

Spoon into bowls and dust with ground cinnamon. Serve warm for a cozy dessert or refrigerate until cold for a refreshing chilled treat.