To the apple puree, add the salt, ground cinnamon, ginger, cloves, allspice, nutmeg, and lemon juice with zest. Cook in a large thick bottomed pot over low heat, stirring occasionally to prevent the apple butter from burning. Make sure you scrape the bottom of the pot while you stir, because the sugar caramelizes in the bottom and there's crust situation. Cook until the puree has thickened, about 1 1/2 - 2 hours. The resulting apple butter situation should be thick and not runny.