Mix the oatmeal with the salt and baking soda in a bowl.
Melt the shortening in the boiling water and add to the dry ingredients.
Mix to form a soft dough.
Sprinkle the work surface thickly with oatmeal.
Turn out the dough and knead well, with the hands covered in oatmeal to prevent sticking, and form into a ball.
Press down a little, keeping the edges as round as possible, then roll out to a round 1/4 inch thick.
Trim the edges by putting a dinner plate on top and cutting around it.
Sprinkle with a little more oatmeal and either bake whole or divide into 8.
Flour a griddle or baking sheet.
If baking on a griddle or in a heavy frying pan, warm the griddle or pan first and then put on the oatcake(s).
Cook until the edges curl slightly.
Crisp the top: side under the broiler.
If baking in the oven, place on the baking sheet and bake toward the top of a moderate oven (325°F) for about 30 minutes.
Cool on a cake rack.