In a cocktail shaker or mixing glass, add the cucumber slices and mint leaves. Gently muddle 6–8 times until cucumber releases juice but don't pulverize the mint; the goal is fragrant oils without bitterness.

Add spirits and sweeteners

Add 2 oz gin, 0.5 oz elderflower liqueur, 0.75 oz fresh lemon juice and 0.5 oz simple syrup to the shaker with the muddled cucumber and mint.

Shake

Fill the shaker with ice (about 1 cup cubed), secure the lid, and shake vigorously for 10–12 seconds until the shaker is frosty and well chilled.

Assembly

Strain

Double-strain the contents into a chilled Collins glass or highball filled with fresh ice using a Hawthorne strainer and a fine mesh strainer to remove small bits of cucumber and mint.

Top and finish

Top the drink with about 2 oz club soda (or to taste) and gently stir once to combine without losing too much effervescence.

Garnish

Thread a cucumber ribbon or wheel onto the rim, add a fresh mint sprig, and finish with a lemon twist expressed over the drink and dropped in.

Serve

Serve immediately while cold and effervescent. Provide a straw or stirrer so the guest can refresh the drink as the ice dilutes.