Success!!! Check out the recipe below.
200g butter, out of the fridge for 20 minutes, just a bit soft, chopped into 3cm cubes
1/2 cup icing sugar
1 1/4 cups plain flour
the finely grated zest of 1 medium lemon
1 largeish egg yolk (keep egg white)
3 egg yolks
1 1/2 cups caster sugar
400ml freshly squeezed lemon juice
You will need a 5cm deep 26 1/2 cm tart tin with a removable base or a 2 1/2 cm deep 29cm tart tin for this recipe. (You will also need a food processor and a beater.) Pastry first - whizz butter, icing sugar flour and lemon zest just until it forms big clumpy breadcrumbs. Add yolk and pulse until it all comes together in a ball. Pat into a big fat disc, flour the top and bottom lightly, wrap in Gladwrap and chill in the fridge for 15 minutes. While it chills, prepare the filling. Beat eggs and yolks with sugar for 5 minutes, until sugar is dissolved (not gritty). Beat in cream, then whisk in lemon juice gently to combine. Pour into a big jug and leave to sit in the fridge while you finish the base.
Remove the pastry from the fridge, sit for 5-10 minutes, then roll out on a floured surface, into a circle a little bigger than your tin. Use a big fish slice or similar if you need to, to unwedge it from the bench. (A wee tip here - when flouring the bench, flour an area as big as you want to roll your pastry...) Now this is a tricky bit - this a soft pastry, lots of butter will keep it short and crisp, but it also makes it a little less amenable when getting it into the tin. Gently roll up the pastry around your rolling pin, and un-roll it over the tin so that it flops roughly into position. (No-one is looking, and if they are shoo them out of the kitchen - this is private cooking business that does not like an audience). Gently squish the pastry into place up the sides of the tin and press gently into the base. Patch up any tears - you will never see them - but you do want to finish with an evenly distributed pastry base. Chill in the freezer for half an hour while the oven preheats to 180˚C (350˚F).
Now - do not fudge this bit - it makes all the difference, gently prick the base of the pastry with a fork and cut out a large circle of baking paper, it needs to come up the inside sides of the pastry. Put it in and fill it with baking beans or rice - it must come at least some way up the sides of the pastry, what you want is to pre-cook it so that it doesn't shrink, and provides firm, non collapsing sides to the tart. Cook for 12 minutes, carefully remove paper and beans/rice, brush with quickly whisked reserved egg white and cook a further 5-7 minutes, until lightly golden. Reduce oven temperature to 150˚C (300˚F) and skim the fluffy bubbly layer off the top of your filling. This gives your tart a very clean, deep yellow appearance like the beautiful tartes au citron you will find in France - you can stir the creamy bit in, and it will taste fabulous, but the top of your tart will have a slightly 'milkier' appearance. (I skimmed off at least 1 1/4 cups - it seems very wasteful, but you can bake it separately in a couple of ramekins at 150˚C (300˚F) for 25 minutes later to make baked lemon cream for 2) Pull base half way out of the oven and gently pour in the filling - by my calculations you should be just about spot on with the amount - you want it to come almost to the top. Gently push back into the oven and cook 45-50 minutes until set but still with a bit of wobble in the middle. Turn the oven off, open the door wide and let it sit there for 5 minutes before removing to cool on the bench, then in the fridge.