01 - Preheat oven to 325°F. Lightly grease a 2-quart baking dish with unsalted butter.
02 - Rinse the uncooked rice under cold running water until the water runs clear, then drain thoroughly.
03 - In a large mixing bowl, whisk together sweetened condensed milk, whole milk, melted unsalted butter, granulated sugar, vanilla extract, ground cinnamon, and salt until fully incorporated.
04 - Stir the rinsed rice and, if desired, raisins or sultanas into the milk mixture.
05 - Pour the mixture into the prepared baking dish, stirring gently to distribute the rice and raisins evenly.
06 - Bake uncovered for 1 hour, gently stirring every 20 minutes to ensure even distribution, until the pudding is set and the top turns lightly golden.
07 - Remove from the oven and let cool for several minutes. Serve warm or chilled, dusted with additional cinnamon if desired.