Peel, core, and chop the apples into 1-inch pieces. Heat the oven to 275°F (135°C).
Combine the apples, apple cider, and salt in a large heavy Dutch oven. Bring to a simmer over medium heat, then cover and cook, stirring occasionally, until the apples are very soft, 25–35 minutes.
Remove from the heat and purée the mixture with an immersion blender until completely smooth (or carefully blend in batches, then return to the pot).
Stir in the brown sugar, cinnamon, cloves, allspice, and apple cider vinegar until evenly combined.
Transfer the uncovered pot to the oven and bake, stirring every 20–30 minutes, until the apple butter is thick, glossy, and deep mahogany, 2–3 hours. Doneness cues: a spoonful should mound softly and a track should hold briefly when you drag a spoon through the surface.
For ultra-smooth texture, blend again briefly. Let cool 15 minutes, then ladle into clean jars. Cool to room temperature, cover, and refrigerate up to 3 weeks or freeze up to 6 months.