Pre-chill a coupe glass with ice water and set aside.
Prepare a grapefruit zest twist and set aside.
Discard the ice water from the chilled glass.
Combine gin, fino sherry, lemon juice, rich sugar syrup, and orange bitters in a cocktail shaker.
Add ice and shake hard for 10–12 seconds.
Fine strain into the chilled coupe glass.
Express the grapefruit zest twist over the surface of the drink to release its oils, then place on the rim as garnish.
Fino sherry is the secret weapon here - its low ABV and briny, nutty dryness effectively replace a portion of the spirit while adding savory depth that plain sugar syrup could never achieve. Use a fresh, chilled bottle of fino as it oxidises quickly once opened.
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