Pre-chill a Collins glass by filling it with ice water and setting aside.
Add 50ml London Dry Gin, 15ml elderflower liqueur, 5ml maraschino liqueur, 30ml fresh lemon juice, and 10ml rich sugar syrup into a cocktail shaker.
Fill the shaker with ice and shake vigorously for 10–12 seconds.
Discard the ice water from the Collins glass and fill it with fresh ice.
Strain the shaken mixture into the glass, then top with 25ml soda water.
Gently stir once to integrate.
Garnish with fresh elderflowers, gypsophila (baby's breath), or a lemon wheel.
Using a rich (2:1) sugar syrup rather than a standard simple syrup keeps the sweetness dialled in at a lower volume, preventing dilution from watering down the delicate elderflower notes - a small detail that makes a noticeable difference in this style of long drink.
My Bar Shelf reads your shelf and shows you every cocktail you can make from what you already own, including Elderflower Collins.