Pit the cherries. This is easiest using a cherry pitter but a straw also works. You can reserve the pits to also add to the infusion or toss them. See notes below.
Wash the cherries using a minimal amount of the vodka. Pour off the vodka.
Add the cherries (and optional pits) to the rest of the vodka directly into the container. Seal and store in a cool, dark place for 3-7 days, remembering to shake it every couple days to help release the cherry flavor. The cherries are delicious, too!
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Notes
The cherry seeds add an almond-like flavor to the vodka that I enjoy, but you can absolutely leave them out. I prefer to add them in separately from the pitted cherries because leaving the cherries whole doesn't allow the flavor to infuse as strongly into the vodka. So whether or not you leave them, still pit the cherries before adding them to the vodka. You can also infuse them separately and mix them back together.If you aren't using the bottle the vodka came in, be sure to sterilize the bottle you are using and then give it a rinse with vodka.