Cream the butter with the icing sugar then beat in the lime zest, lime juice and vanilla.
Mix the flour, corn flour and salt in a large bowl.
Beat the dry ingredients into the wet.
On a piece of baking paper, roll the dough into a 1 ¼ inch log.
Wrap it up in the baking paper and let chill in the fridge for at least an hour.
Slice the dough into ½cm thick slices and place them on a baking sheet, 2cm apart from each other.
Bake in a preheated 170C(375F) fan-forced oven until just lightly golden brown, about 12-15 minutes. Let cool on a wire rack for 4 minutes.
Dredge cookies in icing sugar to coat.