In a large saucepan combine cornmeal, boiling water, and salt. Cook over low heat for 30 minutes, stirring frequently.
Meanwhile, melt shortening in a large skillet over medium heat. Add chopped onion and saute until brown. Add beef and cook just until no longer pink. Stir in tomatoes, pimientos, and cayenne pepper, then remove from heat.
Oil bottom and sides of a 3 quart casserole dish and line with two thirds of cornmeal mixture. Pour in meat mixture, then top with remaining cornmeal. Bake in preheated oven for 2 to 2 1/2 hours.
