Add the apples, water, cinnamon, vanilla bean, and salt to your slow cooker. Set the slow cooker to high and cook for 5 hours, stirring and mashing the fruit halfway through the cooking time.
Open the lid of the slow cooker and cook for an additional 45 minutes to 1 hour until the mixture darkens and most of the liquid evaporates. It should look nice and saucy. Check and stir occasionally. Let cool slightly, remove the vanilla pod (save and wash for another use), cinna-mon stick, and star anise (if using). Transfer to a food processor or blender. Blenduntil you have a buttery silky-smooth purée, emulsifying all those skins. Taste and adjust the seasoning with lemon juice if you like.
If your apple butter is watery after puréeing, put it back in the slow cooker with the lid open for an extra 15 to 20 minutes (or in a saucepot over medium-low heat), stirring occasionally until thick. Transfer to clean jars, seal, label, date, and refrigerate.