In a large pot (I use a 4-quart Dutch oven), combine the apples, water, sugar, cinnamon, vanilla, and salt. Cook over medium heat for about 15 minutes, or until the apples are very soft.
Use an immersion blender to puree the mixture until very smooth. Alternatively, you can transfer the mixture to a food processor or blender, then return the pureed mixture to the pot.
Add the lemon juice and cook over medium-low heat for 15–20 minutes, stirring occasionally, until thickened to your liking. Keep in mind that the apple butter will thicken more as it cools. For an extra smooth texture, pass the mixture through a fine mesh sieve before canning.
Pour the hot apple butter into sterile jars and seal them tightly. Refrigerate overnight before serving. This apple butter is also great for water bath canning if you want to store it for a longer time.