In a small dish soak your raisins in just enough rum to cover. It should be about 2 ounces, if not less. Let sit for at least 10 minutes.
Pour all of the liquid ingredients into a blender, along with the cinnamon, vanilla, freshly ground nutmeg, and drained raisins. (Add the rum too if you're not worried about the alcohol.)
Blend until the raisins are full incorporated and no raisin bits remain.
Pour into a pitcher or other large glass container and chill for at least 1 hour.
Serve cold by itself, or add in a bit of rum to your liking.