Mix flour, yeast, salt and sugar, then add enough water to make a fairly firm dough. Knead vigorously until dough is smooth and elastic - you can do this in a food processor, but it is very therapeutic to do it by hand! Place in a clean bowl, cover, and leave in a warm place for about an hour, or until doubled in size. Knead again, then place on a greased, floured oven-proof plate. Cover, if possible with an oven- proof bowl, and leave for ten-fifteen minutes. Bake in a hot oven (mark 7, 200 C, 425 F) for about 40 minutes, or until it sounds hollow when tapped underneath. This doesnt keep well as it has no fat, but that is seldom a problem!