In a medium saucepan, combine milk, butter, sugar, rice, salt, and cinnamon.
Bring to a simmer and simmer uncovered, stirring frequently, for 30-40 minutes, until rice is tender. Be sure to scrape the bottom and sides of the pan when you stir it. If the mixture appears to dry out during cook time you can add a few splashes of milk. During the last few minutes of cook time, add the vanilla, raisins, and heavy cream and simmer for a couple more minutes. Serve warm or chill. The rice pudding will thicken up after chilling; you can stir in a splash of milk to thin it out again.