Trim outer dry layers from lemongrass stalks, then finely chop the tender inner parts. Combine chopped lemongrass, sugar, and water in a small saucepan.

Bring the mixture to a gentle simmer over medium heat, stirring until the sugar dissolves. Reduce heat and simmer for 8–10 minutes to infuse lemongrass flavor.

Remove from heat, add lemon zest if using, and let steep, covered, for 20 minutes.

Strain the syrup through a fine mesh sieve, pressing on solids to extract liquid. Cool to room temperature. Transfer to a clean bottle and refrigerate. Yields about 100–120 ml; use 15 ml per cocktail.

Rhubarb-Gin Cocktail Assembly

Chill a highball or Collins glass by filling it with ice and setting aside while you prepare the cocktail.

Discard the chilling ice and fill the glass with fresh ice cubes to about three-quarters full.

Measure and pour 60 ml Slingsby Rhubarb Gin into a mixing glass or directly into the chilled serving glass over the ice.

Add 15 ml fresh lemon juice and 15 ml lemongrass syrup to the gin. Stir gently 6–8 times in the glass to combine and slightly chill the mixture.

Top with about 90 ml chilled ginger ale. Pour slowly over the back of a spoon or down the side of the glass to preserve carbonation.

Give a single gentle stir to integrate the ginger ale without flattening it.

Garnish with a lemon wheel on the rim and a bruised lemongrass stalk (lightly smack the stalk on the work surface to release aroma) placed in the glass. Optionally add a rhubarb ribbon or candied rhubarb for visual appeal and extra rhubarb aroma.

Serve immediately with a straw and enjoy. Stir once or twice during drinking to redistribute flavors.