01 - Preheat oven to 325°F. Lightly grease a 2-quart baking dish with butter.
02 - Rinse short-grain rice under cold water until water runs clear, then drain thoroughly.
03 - In a large mixing bowl, whisk together sweetened condensed milk, whole milk, melted butter, granulated sugar, vanilla extract, ground cinnamon, and salt until fully combined.
04 - Stir rinsed rice and, if desired, raisins or sultanas into the milk mixture to evenly distribute.
05 - Transfer the mixture to the prepared baking dish, stirring gently to ensure even rice dispersion.
06 - Bake uncovered for 1 hour, gently stirring every 20 minutes, until set and the surface is lightly golden.
07 - Remove from oven and allow to cool slightly. Serve warm or chilled, finishing with a light dusting of ground cinnamon if desired.