Add apples, lemon juice, sugars, India spice and salt to the bowl of a 6-quart slow cooker and mix to combine. Cover and cook on low for 8-9 hours, until mixture is dark and thick. \nUncover and stir in the vanilla extract. Mix to combine, breaking up the large chunks of apple. Turn slow cooker to high and continue cooking, uncovered, for an additional hour, allowing the mixture to thicken. \nUsing an immersion blender, puree the apple butter until smooth and creamy. Alternatively, blend the mixture in batches using a regular blender or food processor. Let cool slightly. Place in a resealable container and refrigerate for up to 2 weeks. \nEnjoy your apple butter on toast, pancakes, pork chops, or just with a spoon!