during this time make the lime curd (recipe below)
preheat oven to 160c (for fan oven) or 180c for electric oven
grate the zest off all four limes, keep the zest of one lime back for later. then squeeze the juice all four and add it into a pan with the zest, with the sugar and egg yolks, eggs, butter and whisk together over a low heat, stir continuously until it thickens and coats the back of the spoon.
spoon into the centre of two cookies.
mix the remaining lime zest and sugar and sprinkle on top.