Start water boiling for potatoes. (Salt, if desired).
In a mixing bowl, combine all Salisbury Steak ingredients, EXCEPT the ground beef. Then add ground beef and thoroughly mix together. Use a 2-inch food scoop to divide mixture into 12 even portions. Flatten and shape into ½ inch thick round patties.
Add potatoes to boiling water. Cook until fork tender (about 20 minutes).
In a large sauce pan over medium high heat, add formed steaks. Cook on each side about 4 minutes. Remove to a plate and keep warm while cooking the rest of the steaks.
In a large measuring cup, add all onion gravy ingredients, EXCEPT the oil. Whisk together until completely combined.
In same pan used to cook the steaks, add oil over medium heat. While heating up, gently scrap up any bits from the bottom of the pan. Then pour gravy mixture into pan. Let come to a bubble, then whisk occasionally as gravy begins to thicken.
Drain potatoes and add to large mixing bowl. Add melted butter, salt, pepper and heavy cream. Smash and combine until desired level of smoothness.
In a bowl, add a portion of potatoes, and two steaks. Ladle pan gravy over top. Sprinkle with parsley, if desired.