Step 1

Mix ground beef, onion, eggs, 1 tablespoon Worcestershire sauce, parsley, 2 teaspoons salt, garlic powder, onion powder, and 1/2 teaspoon pepper together in a bowl. Split steak mixture into 6 portions and form into patties.

Step 2

Heat a large skillet over medium-high heat. Cook patties, 3 at a time, until slightly browned on one side, about 5 minutes. Flip and cook until other side is browned, about 5 minutes more. Repeat with remaining patties, pouring off any excess liquid. Place Salisbury steaks on a plate and cover with aluminum foil to maintain heat.

Step 3

Melt butter in the same skillet over medium heat. Add mushrooms and cook until golden brown, about 5 minutes. Transfer mushrooms to a bowl, reserving butter in the skillet.

Step 4

Stir flour into the butter until dissolved. Pour in beef broth slowly, stirring until thickened, about 7 minutes. Add 1 teaspoon Worcestershire sauce; cook, stirring frequently, until gravy starts to thicken slightly, about 5 minutes. Add sour cream and season with salt and pepper. Cook, stirring until all sour cream is melted and gravy is light brown, about 2 minutes.

Step 5

Stir mushrooms back into the gravy. Remove from heat and let cool until thickened, about 2 minutes. Ladle gravy and mushrooms over steak patties.