Saute the onion in the shortening until tender and golden brown.
Mix with the mashed potatoes, ground beef, and gravy.
Thin the gravy with a little milk if it is a thick gravy.
Add salt and pepper to taste and any other seasonings or flavorings you prefer.
Add beaten egg yolks and parsley Mix well.
Fold in stiffly beaten egg whites.
Spoon the mixture into a greased baking dish and bake at 350 for about 1 hour. This pie will be light and fluffy!