Preparation Combine sugar and 1/3 cup water in a jar. Cover; shake until sugar dissolves. Combine syrup, whisky, lemon juice, and club soda in a large pitcher. Add 8 cups ice; stir until ice begins to melt, about 1 minute. Serve over ice, garnished with lemon twists, if desired. DO AHEAD: Syrup can be made 3 months ahead; cover and chill.
Preparation Combine sugar and 1/3 cup water in a jar. Cover; shake until sugar dissolves. Combine syrup, whisky, lemon juice, and club soda in a large pitcher. Add 8 cups ice; stir until ice begins to melt, about 1 minute. Serve over ice, garnished with lemon twists, if desired. DO AHEAD: Syrup can be made 3 months ahead; cover and chill.