Make the steaks: in a large bowl, combine the ground beef, shredded frozen butter, egg, breadcrumbs, minced onion, parsley flakes, mustard, garlic powder, salt, and pepper, using your hands. Shape the beef into 5 oval-shaped steaks.
Heat the oil in a large skillet over medium-high heat and brown the steaks for 2-3 minutes on each side, or until brown. Transfer to a plate.
Melt the butter in the same skillet and saute the sliced onions for about 15 minutes or until caramelized and golden brown. Pour in the chicken broth, beef broth, Worcestershire sauce, dried thyme, onion powder, salt, and pepper. Bring to a light boil, scraping the bottom of the skillet to remove all the bits and pieces stuck to it. Add the cornstarch and water slurry and boil until thickened. Return the steaks to the skillet, cover with the gravy, and cook for 10 minutes or until the meat is cooked through.