Combine gin, lime juice and celery seed syrup in a cocktail shaker. Fill halfway with ice and top with a fistful of fresh cilantro. Shake vigorously for 20 seconds. Double strain into a coupe glass. Garnish with lime wheel.
Combine 1 cup (250 mL) each sugar and water in a small saucepan; stir in 2 tbsp (30 mL) celery seed, cover and bring to a simmer over medium-low heat. Cook 5 minutes. Remove from heat and let stand 1 hour. Strain through several layers of cheesecloth; chill before use.
Makes about 1 cup (250 mL)