In a large bowl, mix together the flour and the icing sugar. Rub the butter into the flour and sugar mix using your fingertips, until the mixture resembles texture and appearance of the breadcrumbs.
Make a small well in the middle and add eggs and egg yolks. Using fork, mix the eggs into the flour. Add 1-2 tbsp of ice cold water and using your hands, mix the dough until it comes together. Roll it into a ball and divide in half (you can freeze the other half until you need it for another recipe). Flatten the other half into a disk, wrap in some clingfilm and place in the fridge for at least 30 minutes.
While the pastry is chilling in the fridge, prepare the filling. Place all of the ingredients apart from lemon zest into a large bowl and beat until combined. Sieve the mixture then mix in the lemon zest. Set it aside.
On a lightly floured surface, roll out the pastry into a circle bigger than your tart tin (you want it to overhang from the tin) to a thickness of about £1 coin. Lift the pastry and transfer to your tin. Using your fingers, press the pastry gently into the bottom and sides of the tin. Trim off any excess pastry. Using a fork, prick the base of the tin and put it back in the fridge for 30 minutes.
Heat the oven to 160 C (140 C fan). Line the tart tin with some baking parchment or kitchen foil and fill with ceramic baking beads or some rice or dried beans. Bake for 10 minutes, remove from the oven, discard the parchment/ foil and baking beads and bake for another 20 minutes until lightly golden and biscuity. Remove from the oven, pour the lemon mixture into the tin with pastry and bake for another 30 minutes, until just set. Remove from the oven, and allow it to cool for 10 minutes. Remove the tart from the tin and cool completely before topping up with the meringue.
To make Italian meringue:
In a bowl of an electric mixer, beat the egg whites until stiff peaks. Place the sugar and 3 tbsp of water into a medium size pan over a gentle heat. Once sugar has completely dissolved, turn up the heat and boil syrup, without stirring it, until the mixture reaches 120 C on a sugar thermometer.
Take off the heat and working swiftly, carefully pour the syrup into stiff egg whites, whisking continually at low speed, until the mixture is cold.
Use the meringue to top up your pie with. You can also toast the meringue gently using a kitchen blowtorch.
The sweet shortcrust pastry recipe will make double the amount of pastry needed. Freeze the other half until you need it for another recipe
You can use shop-bought, ready- rolled shortcrust pastry if you don't want to make your own
Italian meringue is much firmer and more stable than traditional meringue, so it works much better for topping up the pies or cakes with it, however, feel free to use your favourite meringue recipe.