You will need a 23cm (9in) cake tin with a removable base, or a rectangular cake tin. First, make the pastry. Place the flour, the butter and the sugar in a food processor and whizz briefly.
Add half the beaten egg and continue to whizz. You might need to add a little more egg - but not too much, as the mixture should be just moist enough to come together. If you're making the pastry by hand, rub the butter into the flour and sugar until it resembles breadcrumbs, then using your hands, add enough beaten egg to bring it together.