For the Salisbury Steak:
Combine all the ingredients for the steaks in a large bowl and mix well.
Form into 6 oval patties about 1-inch thick and place them on a cookie sheet lined with parchment paper. Bake at 375 F for 25-30 minutes.
For the Gravy:
Melt butter in a large skillet. Add mushrooms, and cook on medium high until golden brown. Add onions and cook for 5 minutes over medium heat until golden and soft. Add broth and Worcestershire sauce, stir and cook for 3 minutes, stirring to scrape any bits off the bottom of the pan. Add sour cream, stir well and remove from heat. (If you want a thicker gravy, cook on low for an extra 5 minutes). Season with salt and pepper to taste.
Serve gravy over warm Salisbury Steaks with fresh parsley for garnish, if desired.
Serves 6