Cook the apples: Place chopped apples and cider in a large pot or slow cooker. Cover and cook until apples are very soft (about 25-30 minutes on the stove, or 3-4 hours on high in a slow cooker).
Blend: Use an immersion blender to purée until smooth (or transfer carefully to a blender in batches).
Spice and sweeten: Stir in brown sugar, spices, and salt.
Slow cook: Simmer uncovered over low heat (or on low in a slow cooker) for 2-3 hours, stirring often, until thickened and dark brown.
Finish: Stir in vanilla. Let cool before transferring to jars.