In a mixing glass, combine syrup and whiskey with a few ice cubes. Stir gently to chill.
Place a large ice cube in a rocks glass and let it rest for a few minutes to prevent cracking.
Strain the cocktail over the ice, aiming for the side of the glass.
Twist the orange peel over the drink to release its oils, then rub it around the rim before adding it to the glass.
Garnish with a cherry and finish with a couple of dashes of bitters.
Notes
Too sweet? For a less sweet cocktail, use ¼ ounce of simple syrup. Too strong? Add a splash of water or wait a moment before sipping to allow the ice to melt.