In the crock of your slow cooker, combine the apples, sugar, cinnamon, and lemon juice.
Top the mixture with the cinnamon stick and vanilla bean.
Cover and cook until apples are very soft and mushy, on low for 4 hours, or on high for 2 hours. Stir occasionally. If the sauce seems too thick add a little water each time you stir.
Remove the cinnamon stick and vanilla bean and using either an immersion blender (be careful, sauce is hot!), a potato masher, or for very smooth sauce, a food mill, smash or blend to desired consistency.
At this point if you need to add more water or sugar (if you want a sweeter sauce), do so, cook for another 5 or so minutes.
Refrigerate in airtight containers for up to one week, or freeze for up to 3 months.
