Mix flour, sugar, BP and butter to the consistency of fine bread crumbs with fingertips.
Break the egg into a well in the centre.
Mix with a fork until soft crumbly dough.
Knead with the hands inside the bowl and then out onto a floured board. Don’t play with the dough too much. Keep it cool.
Divide in half.
Roll out half and place in a buttered dish. Be careful not to stretch the pastry.