1Add beef with meat trimmings and bones in stock pot with cover with cold water; add onion, carrot and celery. Let simmer several hours; strain off broth, reserving. Remove beef slices and return to stock pot and add reserved broth; simmer until the beef is tender. Season with salt and pepper. Pour into a baking dish; cover with a round of potato crust in which there is an opening; bake until the crust is done, 15 minutes.
2Potato crust: Sift together flour, salt and baking powder. With the tips of your fingers work in shortening, then the mashed potatoes; add enough milk to make a soft dough, turn on to the board, handling as little as possible and pat and roll out to fit the dish.