Take two cups of self-rising flour and sift in dry a scant teaspoon of baking soda. Work thoroughly into this about 1/3 a cup of cold vegetable shortening. Mix with the fingers until it has an almost granular texture. Then, working quickly, stir in enough buttermilk to make a sticky dough. Throw this dough out on a generously-floured surface, sprinkle with a scant more flour and knead once or twice, only enough to make it manageable mass, then roll out thick, about half an inch, and cut into large rounds, at least 3″. Be sure to cut them with a sharp edge that won’t pinch the dough: a Mason jar just won’t do it. Again, work quickly so that the dough doesn’t get warm; the soda has to work in the oven. Place the biscuits together, just touching, in a lightly greased skillet (or a thick metal pan); the light oiling ensures a nice bottom crust. Pop them in a very hot oven for about a quarter an hour. You want them golden-brown and fragrant; brush lightly with butter while hot.