Step 1

Purée apples, parsley, 5 celery stalks, and 3 cups water in batches in a blender. Strain through a fine-mesh sieve into a pitcher, gently pressing with a spoon to extract as much liquid as possible (alternatively, run apples, parsley, and celery through a juicer and mix with 3 cups water). Stir in vinegar, salt, and ¼ tsp. pepper and add more celery stalks.

Step 2

To serve, pour 4 oz. juice and 1 oz. gin, if using, into an ice-filled glass and sprinkle with pepper.