The lemon tree in our garden is full of fruit right now and it is a challenge to make good use of the crop. We use a lot of lemon juice in our everyday cooking,we preserve lemons- stay tuned  for some really good recipes-, we freeze lemon juice ice cubes that keep for several months, and we bake. We are always trying out new recipes and after exhaustive research our preferences are a lemon cake and this rather rich Heston Blumenthal lemon tart for special occasions. Our advice? If you do not have a forthcoming special occasion, improvise one and bake this tart! Serves 10-12 For the pastry 300g Plain flour  150g Unsalted butter 120g Icing sugar 1/2 tsp Salt 3 Large egg yolks  Zest of 1/2 lemon, finely grated Seeds from 1/2 vanilla pod 1 egg for the egg wash For the filling Finely grated zest and juice of 5 lemons  390g White caster sugar 300g Double cream 9 large eggs and 1 large egg yolk To finish and serve 80g Unrefined caster sugar Creme fraiche …