Sift the flour into a bowl then add the butter. Using your fingers rub the butter into the flour until it resembles breadcrumbs. Grate (shred) the cheese then stir it into the bowl. Separate the egg yolk from the egg white (you don't need the white) and add the egg yolk and cold water to the mix. Knead together to create a firm dough.
Turn the dough onto a lightly floured board or other flat surface and roll it out to about ¼" (5mm) thickness. Using a plain-edged cookie cutter or upturned eggcup (or similar) cut the dough into rounds of about 1½" (3.5cm). Place these well apart on a lightly greased baking tray and bake in a preheated moderately hot oven (Mk 6 - 400ºF - 200ºC) for 10 minutes. Remove from the oven and allow to cool on a wire rack.