With you hands, mix all of the ingredients for the Salisbury Steaks, except the butter. Form 8-10 oblong patties.
Fry the patties in 1/4 cup of butter until cooked to your preference. Do not crowd the patties, prepare them in batches as necessary. Remove from heat.
In the same skillet, add additional 1/4 cup of butter, sliced onions and mushrooms. Cook until soft (about 15 minutes).
Add flour to the butter, mushroom, onion mixture. Slowly add the flour so that it is completely absorbed by the butter to create a paste-like consistency.
Slowly add the broth to mixture. Make sure to add it slowly so that there are no lumps. You cannot get lumps out later. Bring to a boil. Reduce to a simmer and allow to thinken.
Add patties back to the gravy and allow them to cook together over low heat for 20 minutes to an hour or longer.
