Process until the pieces of butter are about pea sized.Add the egg and pulse on low until it resembles bread crumbs. Be careful not to overprocess.

Finally, with the processor on low, dribble in the cold water and let it continue blending until it start to form clumps.

Turn the pastry dough out onto a clean surface and pull it together with your hands, kneading it just enough to make it mostly smooth. Dust the surface and the top of the dough with a little flour, then roll out to about 11 inches round.

Transfer the dough to a 9 inch pie dish, by first folding it over the rolling the pin then lifting and laying it out over the dish.

Press the pastry dough down into the corners all the way round. Trim the sides with a sharp knife, then crimp the edges all the way round. Transfer to the fridge to chill for a minimum of 2 hours or overnight.

Use a fork to prick the pastry base all over. Line the pie crust with baking paper, then fil with pie weights (or rice). Fill it quite full.

Bake for 20 minutes then carefully remove the paper and pie weights and bake a further 15 minutes.

Remove from oven and allow to cool completely before going onto the filling.

Place the saucepan back over the heat and cook for a further minute or until the temperature reaches 71C / 160F on a digital or instant read thermometer.

Pour lime filling into base then let it cool at room temperature for 30 minutes to set up a bit. This will make it easier to spread the meringue. Keep in mind, the filling should still be warm when you add the meringue so get straight onto making that.

Whisk egg whites in clean glass bowl or the bowl of a stand mixer on medium-high speed, until soft peaks.

Sift over the cornflour and mix on low to combine. Turn the mixer up to medium and add the sugar 1 tablespoon at a time, counting to 20 seconds after each addition.

Once all the sugar is in, give the bowl a scrape down the sides with a spatula to get any sugar crystals that may be stuck there. Now beat on high until the meringue is glossy with stiff peaks and rubbing a little between your fingers, you can’t feel any sugar grains.

Scoop the meringue out onto the filling and gently press out a little towards the sides, keeping a hill in the middle. Make sure to go all the way to the sides though, touching the crust. Create peaks or a swirly pattern with your spatula.

Let it cool for 2 hours at room temperature, then place in the fridge uncovered to cool completely (3-4 hours) before you slice it. As long as your meringue is all the way to the edges, it will be fine in the fridge overnight like this.