Wash the apples very well (I like to leave the skin on. If you don't have a blender that will handle pureeing the skin then peal). Dice the apples and add to saucepan. Cut vanilla bean down the middle and scrape out seeds with a knife and add to saucepan along with the vanilla bean
Add water to the pan so it comes approximately half way up the apples. Cover and cook until tender.
Discard vanilla bean and puree in a blender