Preheat the oven to 180'C.
Scrape the seeds from the vanilla pod, cut the butter into small cubes and place in a bowl. Add the flour and the sugar and rub together with the tips of your fingers until the mixture resembles breadcrumbs. Add the egg and bring the mix together until it forms a ball. Knead with the palm of your hand until smooth, wrap in cling film and rest in the fridge for at least 30 minutes.
Roll the pastry out between 2 sheets of baking paper to 5mm thick. Grease the inside of the tart cases with soft butter and dust with plain flour.
Transfer the pastry to the tart case and trim the edges. Line the inside of the tart with baking parchment and cover with baking beans. Transfer to the oven and blind bake for 20 minutes until golden brown. Once cooked, check the pastry case for any small cracks and fill with any left over pastry if necessary.
Reduce the oven temperature to 120'C.
To make the mixture, whisk together the whole eggs and the sugar. Add the zest and juice of the lemons and then mix in the double cream.
Pour this mixture into your tart case and cook in the oven for 30 minutes. The filling should wobble when you take it out. It will solidify further as it cools.
Dust the tart with icing sugar once it is set and caramelise with a blow torch or under a very hot grill.
«Vary the flavours in the tart by replacing the lemon zest with orange.»