01 - Preheat oven to 325°F. Lightly grease a 2-quart baking dish with butter.
02 - Rinse rice under cold running water until water runs clear. Drain thoroughly.
03 - In a large bowl, whisk together sweetened condensed milk, whole milk, melted butter, granulated sugar, vanilla extract, ground cinnamon, and salt until fully combined.
04 - Fold in rinsed rice and raisins, if using, ensuring even distribution.
05 - Pour mixture into the prepared baking dish. Stir gently to distribute rice evenly.
06 - Bake uncovered for 1 hour, gently stirring every 20 minutes to prevent clumping and ensure even cooking. The custard should be set and the surface lightly golden.
07 - Remove from oven and allow to cool slightly. Serve warm or chilled. Sprinkle with additional ground cinnamon if desired.