Pour the vodka and cranberries into a large bottle and add some rock candy. I recommend a small amount at first, 3 - 5 pieces, if the cranberry vodka is not sweet enough after ripening, you can add something more.
Let it rest for approx. 2 - 3 months, occasionally turning the bottle upside down from time to time.
Then taste whether it is sweet enough, sweeten if necessary and enjoy.