For the pastry, with a wooden spoon, beat butter and icing sugar till mixed and there are no sugar lumps. Shouldn't take more than a minute.
Then beat in in the eggs, still with the wooden spoon. Don't worry if you can't/don't get a smooth liquid.
Add the flour and and fold in with the wooden spoon.
When you have gone as far as you can with the spoon, work the pastry with your fingertips till the mix comes together and is relatively smooth.
If needed, add water, 1 tbsp at a time as needed and lightly bring it all together. Knead it very slightly and gently to smooth it all out (do not overwork the pastry).
Flatten it, wrap in clingfilm, and chill for 30 mins.
Lightly flour a work surface, a chilled marble or granite slab would be perfect, to keep the pastry cold. Roll the pastry out to about 2-3cm/1" thickness.
Lift the dough and place it in a 23cm (9") loose bottomed tart tin. This is easier done if you roll part of of the dough onto the rolling pin first and lift it up with the pin. Make sure the pastry is neatly tucked in all around. Long nails, be careful!
Cut off the overhanging pastry, leaving a slight hang for shrinkage if you want. Prick the pastry all over and chill again for 30 mins. I know this is time consuming but you can go off and do stuff in that 30 mins.
Turn oven on to 180˚/375˚F and place a baking sheet on the middle shelf. This is to ensure the bottom of the pastry cooks evenly too. After 30 mins, line pastry with baking paper, fill with beans/rice (ceramic baking beans are perfect) and bake on the hot baking sheet for about 12-15 mins. You need to check this as all ovens are different.
Remove the baking paper & beans and bake for another 3 mins. Brush the pastry all over with the beaten egg yolk & bake again for 2 mins. this forms a seal & stops the bottom of the pastry getting soggy from the filling.
Leave to cool for at least half an hour before removing from the tin. Remember hot pastry is soft.
For the filling, turn oven up to 190˚C/375˚F. This is the easy part!
Gently hand whisk the eggs and sugar in a large bowl (over whisking will result in too many bubbles/foam, you don't want that).
Add the cream, whisk, then add the lemon juice. Some people like to add lemon zest but I don't like bits in my tart!
Carefully pour the mix into the case & bake for about 20-25 mins. Serve at room temperature, dusted with icing sugar.
Notes
Total time does not take into account the chilling of the pastry, which is hands off time.