Step 1

Chill a highball glass.

Step 2

Roll the lemon firmly against a countertop or cutting board for 5 seconds or so, releasing its oils, then cut a thin wedge out of it. Squeeze the wedge over the chilled glass, then drop it in.

Step 3

Fill the glass two-thirds full with large ice cubes. Pour the gin over the ice, then add the tonic syrup. Measure out 3 1/2 ounces of the club soda and pour it into the glass, using a bar spoon to stir in it in.

Step 4

Gently roll the honeysuckle flowers between your fingers. Rap the tarragon sprig firmly once or twice against your palm to release the leaves' aroma. Drop the flowers and sprig into the glass.