How to Make It
Combine sugar, 1 cup water, and 1 rosemary sprig in a small saucepan. Bring to a simmer over medium-high. Remove from heat, and cool completely. Discard rosemary. Chill until ready to use. (Mixture will keep indefinitely in an airtight container in the refrigerator.)
Remove leaves from 1 rosemary sprig; chop. Sprinkle evenly among 4 compartments of a large ice cube tray. Pour 1/2 teaspoon of the whiskey and 1 drop of the cherry bitters in each of the 4 compartments; fill each with water. Freeze until frozen, at least 6 hours.
In each of 4 old-fashioned glasses, place 1 rosemary ice cube, 1 1/2 teaspoons to 1 tablespoon of rosemary syrup, 4 drops of the cherry bitters, and 1/4 cup of the whiskey. Rub lemon peel strip on the rim of each glass. Garnish each with 1 lemon twist and 1 rosemary sprig.
The total time includes 6 hours of freezing.