Preheat the oven to 170ºC/Gas Mark 3. Line two baking sheets with greaseproof paper.
Cream together the butter and sugar. Sift in the flour and mix in with the grated lemon zest. Work in the lemon juice and mix again to form a stiff biscuit mix.
Spoon into a piping bag fitted with a star nozzle and pipe small swirls onto a baking sheet, well-spaced apart as they do spread. When you lift up the nozzle from piping each swirl, use a knife to trim the biscuit mixture neatly.
Bake in the oven for 12-15 minutes or until lightly golden and cooked. Leave to cool on the baking sheet for about a minute, then transfer to a wire rack to cool.