Step 1: Prepare the apples. Peel, core, and chop all the apples into roughly 1-inch pieces. The size doesn't need to be perfect as they will cook down.
Step 2: Combine ingredients. In a large, heavy-bottomed pot or Dutch oven, combine the chopped apples, granulated sugar, apple cider (or water), ground cinnamon, nutmeg, cloves, and allspice. Stir well to combine.
Step 3: Start cooking. Bring the mixture to a gentle boil over medium-high heat, stirring frequently. Once boiling, reduce the heat to low, cover the pot, and simmer for 30 minutes, allowing the apples to soften.
Step 4: Continue simmering. After 30 minutes, remove the lid. Continue to simmer the apple mixture on low heat, stirring every 15-20 minutes, for approximately 3 to 4 hours, or until the apples have completely broken down, the mixture is very thick, and it has darkened in color. The goal is a rich, concentrated flavor and thick consistency.
Step 5: Puree until smooth. Once the apple butter reaches your desired consistency, remove the pot from the heat. Use an immersion blender directly in the pot to puree the apple butter until perfectly smooth. Alternatively, carefully transfer batches to a regular blender or food processor and blend until smooth (be cautious with hot liquids).
Step 6: Finish and store. Stir in the vanilla extract (if using) and apple cider vinegar. Taste and adjust spices or sweetness if needed. Transfer the hot apple butter to clean, sterilized jars. Allow to cool completely before sealing and storing in the refrigerator for up to 3 weeks, or freeze for longer storage. For shelf-stable storage, follow proper water bath canning procedures.