Place rosemary leaves from one sprig into a cocktail shaker. Pour in the lemon juice and maple syrup. Use a muddling tool or a wooden spoon to muddle the rosemary leaves. Fill a cocktail glass with ice.

Pour bourbon into the cocktail shaker and gently stir to dissolve the maple syrup. Strain the cocktail into the prepared glass and top off with club soda. Garnish with the remaining sprig of rosemary.