Sift flour and salt together. Cut in butter. Gradually add water and stir until pastry holds together. Roll out to 1/8 inch thickness. Spread half of dough with part of grated cheese. Fold in half. Roll out again. Spread cheese on half; fold and roll again. Brush top with egg white. Sprinkle with remaining cheese and poppy or caraway seeds. Cut out with a biscuit cutter. Bake for 10 or 12 minutes in 450ºF. oven.