Preheat the oven to gas 4, 180°C, fan 160°C.
Put the flour, caster sugar, cubed butter and half the lemon zest in a food processor and pulse to fine breadcrumbs. Add the lemon juice and gin, ½ tbsp at a time, pulsing between additions until a dough forms. Wrap in clingfilm and chill for 1 hr.
Line 2 large baking trays with nonstick baking paper. Using a 6cm fluted cookie cutter, cut out 20 rounds and transfer to the trays.
Bake for 6-8 mins until lightly golden. Remove from the oven and leave to cool for 5 mins on the trays. Transfer to a wire rack to cool completely.
To decorate, drizzle with the chocolate and scatter with the lemon zest.