- Place the peeled, cored, and quartered apples into a large pot. Add the lemon zest, the lemon juice or vinegar, cinnamon stick, sugar, water and salt.
- Bring to a boil on high heat, then lower the temperature, cover the pot, and maintain a low simmer for 15-20 minutes, until the apples are completely tender and cooked through.
- Once the apples are cooked through, remove the pot from the heat. Remove the cinnamon stick.
- Use a potato masher to mash the cooked apples in the pot to make a chunky applesauce. For a smoother applesauce you can either run the cooked apples through a food mill, or purée them using a stick blender or a standing blender. (If you use a standing blender, do small batches and do not fill the blender bowl more than halfway.)
- Last but not least, add the butter and mix it until totally melted and incorporated.