First make the syrup. Soak the ginger in just enough cold water to cover (this softens the skin and makes it easier to peel), then drain, peel with a teaspoon and slice into fairly thin coins.
Blend with 20ml water, then strain through a fine sieve, ideally lined with muslin.
Measure the resulting ginger liquid (you should end up with about 40ml), then add equal parts honey and stir to dissolve.
To build the drink, put the syrup and lemon juice in a shaker half-filled with ice, add the gin and shake as hard as you can.
Strain into a chilled rocks glass filled with fresh ice, drop in the lemon slice and serve.
