Place the ginger syrup in a cocktail shaker, along with all remaining ingredients and plenty of cubed ice. Shake hard for about 20 seconds, then double-strain (through a Hawthorne strainer and into a fine-mesh sieve) into two prechilled martini glasses. Garnish with a piece of crystallized ginger. Serve at once.
To make the ginger syrup, place the ginger, sugar and water in a blender. Blitz for about 45 seconds, until fully combined. You will make about 1 1/4 cups of syrup, which can be kept in the fridge, or frozen, for future use.
Recipe from: Ottolenghi, Yotam and Ramael Scully. Nopi. Appetite, 2015.