For the Salisbury Steaks:

1. Preheat the oven to 375 degrees Fahrenheit.
2. Combine all of the steak ingredients in a medium sized bowl and mix well.
3. Form into 6 oval patties, about 1 inch thick, and place them on a cookie sheet.
4. Bake for 18 minutes, or until the patties are cooked through.

For the gravy:

1. Melt the butter and bacon fat (if using) in a large skillet.
2. Add the mushrooms and cook on medium high heat until golden brown (about 3 minutes per side.)
3. Add the onions and cook for 5 minutes over medium heat, until golden and soft.
4. Add the broth and the Worcestershire sauce, stir and cook for 3 minutes, stirring to scrape any bits off of the bottom of the pan.
5. Add the sour cream, stir well, and remove from the heat. (if you want a thicker gravy you can cook it on low for a 5 extra minutes to condense it.)
6. Season with salt and pepper to taste.
7. Serve over the warm Salisbury Steaks with extra parsley for garnish if desired.