In a medium bowl, cover cherries with boiling water; let stand for 5 minutes. Drain well.
Meanwhile, in a large saucepan, melt butter and chocolate pieces over medium-low heat, stirring constantly. Whisk in the powdered sugar, milk, and vanilla until smooth. Stir in the cherries. Spoon over cheesecake or ice cream. Store leftovers in a covered container in the refrigerator for up to 1 week.