Place everything into a large pot EXCEPT for the sweetened condensed milk and butter over medium high heat. Stir often as it comes up to a low boil.
Once beginning to boil, reduce the heat down to low. Simmer, stirring often, for 15-20 minutes. You'll know it's done when the rice is tender and the milk has mostly been absorbed. It should still be creamy, but if you need to, you can stir in some additional milk until it reaches your desired consistency. Keep it mind that it will continue to thicken as it sits and cools (especially if you are going to let it chill in the fridge before eating... it will become extremely thick).
Remove the pot from the heat, then stir in the butter and sweetened condensed milk. That's it! Either serve warm or refrigerate in a tupperware for later if you prefer it cold.
