Add bourbon, lemon juice, and rosemary simple syrup.
Shake for about 10–15 seconds.
Strain into a rocks glass with fresh ice.
Top with club soda.
Garnish with a fresh rosemary sprig or smoked rosemary if desired.
Notes
Always use fresh lemon juice for the best flavor. Adjust the rosemary syrup to taste for more or less sweetness. Smoked rosemary can add an extra aromatic layer to the drink.