dark chocolate, couverture • milk chocolate, couverture • (5.1 oz, about 3/5 us cup) heavy cream • (0.7 oz, 1 Tbsp) glutinous starch syrup • (0.4 oz, 1 Tbsp) unsalted butter, room temperature • rum • dark chocolate, couverture, for melting • dark chocolate, couverture, finely chopped • (a small amount of dark chocolate, spare)