Prepare pie crust mix and roll out to a 10 x 14 inch oblong.
Saute onions and mushrooms and let cool slightly. Add to them the bread crumbs, eggs, bitters and salt. Mix with ground round.
Place mixture on the pie crust and shape into a loaf. Moisten edges of pie crust and wrap completely around meat, leaving a ½ inch hole in the top of the crust.
Place seam side down on cookie sheet and bake at 350 degrees for 1½ hours.