To make the pastry, put the flour, sugar, butter and a pinch of salt into a mixing bowl and rub together with your fingers until you have rough crumbs and no butter lumps bigger than the size of a pea. Mix the vinegar with 6 tbsp of ice-cold water, then use a round-bladed knife to quickly mix most of the liquid into the flour. Use your hands to bring together the dough into a shaggy ball, kneading as little as possible. Dribble over the last of the water if you have too many dry bits. Knead a couple of times on a worksurface to smooth the dough, then halve into 2 round discs. Wrap in clingfilm and chill for 2 hours.