Cut the liver into cubes and pan fry in 2 tablespoons of the bacon fat. Pick over and wash the oysters. Place half of the liver in a 1 1/2 - 2 quart casserole and place oysters on top of liver. Sprinkle with salt and pepper. Place bacon on top of oysters. Cover with remaining liver cubes and pour in the tomato sauce. Mix the cracker crumbs with remaining bacon fat and sprinkle over top of casserole. Bake at 350ºF. for 30 minutes. Serves 4