Simmer apples, lemon juice, cinnamon stick (if using), sea salt, and water, in a medium saucepan, over medium-low heat, stirring occasionally, for 30 to 40 minutes, until apples break-up and become a thick sauce. 

Alternatively, cook apples, lemon juice, cinnamon stick (if using), sea salt, and water in a slow cooker on LOW, for 4 hours, stirring once or twice during cooking.

Cool applesauce, then transfer to a covered container and store in the refrigerator for up to 3 days or freeze up to 2 months.