Take two cups of self-rising flour and sift in dry a scant teaspoon of baking soda. Add 1/3 cup cold vegetable shortening, and mix thoroughly with your fingers until granular.
Working quickly, stir in enough chilled 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, no more than enough to make a manageable mass. Roll out thick, about half an inch, and, using a sharp edge, cut into large rounds, at least 3″. Again, work quickly so that the dough doesn’t get warm; the soda has to work in the oven.
Place the biscuits–just touching–in a lightly greased skillet or thick metal pan. Pop them into a very hot oven for about a quarter an hour until golden-brown and fragrant. Brush with butter while hot.