Heat a large saute pan, add the reserved pork fat and cook until it renders, 5 min or so. Add vegetable oil if required and add the pork, toss in the salt and sear until browned. Return to the bowl. Lower heat, add the shallots, saute until soft, then add the apple and garlic, saute briefly, add sherry. Cook a few minutes until reduced, add 3/4 cup of the stock, stir, return the meat to the pan, season with salt, cover and cook on low 30 min.