To prepare the crust, sift the dry ingredients together twice. Combine them in a mix­ing bowl with the shortening and milk, and mix thoroughly with a wooden spoon. Flour a board or marble pastry surface and a rolling pin. Knead the dough by hand for 4 to 5 minutes, then roll it out to a thickness of ½ inch. Invert the pie pan you will be using and press it into the dough to mark a circle. Cut out the circle of dough with a sharp knife. If it appears a bit damp, flour it lightly. Set aside while preparing the filling.

Fry the chopped onion and the bacon squares together in a small heavy skillet or sauté pan until the bacon is moderately crisp and the onions are soft. Grease a 9-inch pie pan with butter. Place half the drained oysters on the bottom and sprinkle with half the onion, bacon, parsley, salt, black pepper, and cayenne. Add ¾ teaspoon of the lemon juice. Make a second layer with the remaining oysters and cover with the remaining seasonings. Pour the melted butter over the top, then cover with the ½-inch-thick round of biscuit dough. Rub the crust with butter. Cut six 1 ½-inch slits in the crust, radiating from an uncut circle 2 inches wide at the center, then bake for 15 minutes in a preheated 450° oven.

Serve in wedges, spooning about 2 teaspoons of the liquid over the crust of each piece.