1. Preheat your oven to 325°F (165°C). Grease a large baking dish with butter or a non-stick spray.
2. In a medium saucepan, bring 2 cups of water to a boil. Add the rice and a pinch of salt, then reduce the heat to low. Cover and let it simmer for 15-20 minutes or until the water is absorbed and the rice is tender.
3. In a large mixing bowl, combine the cooked rice, sweetened condensed milk, whole milk, vanilla extract, and ground cinnamon. Stir in raisins if using.
4. Pour the mixture into the prepared baking dish, spreading it evenly. Sprinkle a little extra cinnamon on top for that warm, inviting look.
5. Bake for 45-50 minutes, stirring every 15 minutes to ensure even cooking. The pudding should be thickened and the top lightly golden when ready.
6. Let it cool slightly before serving, allowing the flavors to meld together beautifully.

From my experience, patience is key here. Stirring the pudding as it bakes ensures that it remains creamy and delightful.