Preheat the oven to 300 degrees F. Combine the apples, cider, sugar, lemon juice, cinnamon, allspice, ginger, cloves and salt in a Dutch oven or large, heavy pot and bring to a simmer over medium-high heat. Reduce the heat to medium and simmer, partially covered, until the apples are very tender, about 25 minutes. Turn off the heat and puree using an immersion blender or in batches in a regular blender (be careful when blending hot liquids).
Transfer the pot to the oven. Bake, uncovered, stirring every 20 minutes so that the bottom does not burn, until the mixture is very thick and a rich brown caramel color, about 3 hours. Cool completely.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.