Make this for our Sticky Rice Balls.
Put plums in a nonreactive bowl; set aside. Stir together vinegar, sugar, 1 cup water, shiso leaves, the spices, and the chile in a medium saucepan. Bring to a boil. Pour over plums; let cool completely. Cover with plastic wrap, and refrigerate at least 8 hours, or up to 1 week. Just before serving, cut plums into 1/2-inch pieces. Discard cinnamon stick and chile.