Make the pastry. Place the flour and butter in the food processor and gently mix until it resembles breadcrumbs.
Add the icing sugar and cinnamon and mix through.
Add the egg yolk and the milk and mix until it starts to form a dough.Take the dough out of the machine and shape it into a block about 1cm thick, this will make it easier to roll out.
Rest in the fridge for at least 1 hour.
Take a 25cm flan/pie dish and roll out the pastry between two sheets of greaseproof paper so that you don't add any extra flour. When the pastry is rolled out big enough to cover the tin lay the pastry over the tin, pressing it into the sides and base of the tin.
Leave the excess pastry overhanging the edge, this will help with shrinkage. Trim the pastry a little if necessary.
Place the pastry case in the fridge for 30mins to chill a little. Pre-heat the oven to 180C Fan/200C and line the pastry case with baking parchment and baking beans. Blind bake the pastry for 15 minutes. Then remove the baking beans and baking parchment and return to the oven for 5 minutes.
Check the pastry over to see if it needs any of the cracks patching use some raw pastry and fill the holes. Take the egg wash and brush it all over the pastry and bake for another 15 minutes.
When the pastry is golden, remove it from the oven.
To make the lemon custard, crack the eggs into a large bowl and beat together using a fork, trying not to incorporate too much air while doing so. Add the sugar, zest of 1 of the lemons and juice of all 4, and finally the cream. Mix together thoroughly, then set aside for 10 minutes. If after this time any froth appears on the surface, spoon off and discard. Pass through a sieve, straining into a large jug or something that can be poured from easily.
Plce the cooked tart still in its tin on a baking tray and place it in the middle shelf of the preheated oven.Pull the shelf out and carefully pour the lemon custard into the pastry case, filling as close to the top as you can. If any bubbles rise to the surface they can easily be popped by running the flame of a blow torch over the surface, but this isn't a necessity. Gently ease the shelf back into the oven, close the oven door and bake for 35 minutes.
Whenready the tart should have a sliht wobble towards the centre. If when gently shaken you feel it is still rippling towards the outer part of the tart, bake for a further 10 minutes and then re-check. The tart can go from being seemingly under cooked to being set solid in no time so be vigilant. Once you are happy with the consisitency removefrom the oven, leave the tart in its tin and leave it to cool completely. It will continue to set further.
Whisk the egg whites in a clean bowl of an electric mixer.
Place the sugar and water in a saucepan over a medium heat and boil until it reaches 121C.
Gently pour the boiling syrup into the meringue and have the whites whisking on a slow speed while this is happening.
After all the syrup has been added, increase the speed to maximum and whisk the egg whites until they are cool to the touch.
When the meringue is ready and at stiff peak stage put it in a piping bag with a star nozzle attached and pipe meringue in patterns or blobs.
Using a chef's blowtorch, cook the top of the meringue. You can then serve the lemon tart immediately or store it in an airtight container.
It's not advised to store this in the fridge as the pastry will become soft and the meringue will break down.