Here is May's original recipe, as reprinted by David (by gallon here May means 7 lbs):

Take a gallon of fine flour, and a pint pf good new ale barm or yeast, and put it to the flour, with the whites of six new laid eggs well beaten in a dish, and mixt with the barm in the middle of the flour, also three spoonfuls of dine salt; then warm some milk and fair water, and put to it, and make it up pretty stiff, being well wrought and worked up, cover it in a bowl or tray with a warm cloth till your oven be hot; then make it up either in rouls, or fashion it in little wooden dishes and bake it, being baked in a quick oven, chip it hot.