Place the apple slices in a clean, 1 quart mason jar. Add the cinnamon stick. Pour in 1 ½ cups of a neutral-tasting gin. (I recommend Beefeater or Aviation.)
Tightly cover the jar and set it aside in a cool place out of the sunlight. After 2 days, remove and discard the cinnamon stick. Let the apples infuse for an additional 3-5 days.
When your infusion is ready, place a fine mesh sieve over a bowl, line the sieve with cheesecloth or a coffee filter, and pour the mixture through. Discard the apples.
Enjoy the gin!