Preparation In chilled cocktail shaker or pint glass, pour club soda over sugar cube. Using muddler or back of large spoon, gently crush sugar cube. Swirl glass until sugar dissolves, 20 to 30 seconds. Add bitters, whiskey, and ice, and stir until well chilled, about 20 seconds. Strain into chilled double old-fashioned glass. Squeeze orange and lemon peels over glass, making sure oils fall into glass; discard peels and serve.
Preparation In chilled cocktail shaker or pint glass, pour club soda over sugar cube. Using muddler or back of large spoon, gently crush sugar cube. Swirl glass until sugar dissolves, 20 to 30 seconds. Add bitters, whiskey, and ice, and stir until well chilled, about 20 seconds. Strain into chilled double old-fashioned glass. Squeeze orange and lemon peels over glass, making sure oils fall into glass; discard peels and serve.