Cut the freshly harvested chinottos into small pieces (quarter) and place in a large bottle or mason jar together with the sugar and mint leaves. Top up the whole thing with the plum water (or a neutral-tasting alcohol, e.g. grain). Let the approach draw through for at least 2 - 3 months in a cool and dark place.
Then the liqueur can be filtered through a fine fleece. Filled in a decorative bottle, a few chinotto wedges and a mint leaf on top, make a great and homemade souvenir.