Add the ground beef, breadcrumbs, dry mustard, onion powder, garlic powder, salt, pepper, ketchup, and egg to a large bowl and mix until well combined.
Divide the mixture into 4 evenly sized patties around ¾ inch thick.
Heat the olive oil in a large pan or cast iron skillet over medium-high heat. Add the patties to the pan and cook, undisturbed, for 2-3 minutes per side until they are browned. Transfer to a plate and set aside.
After searing your patties do not wipe the pan! We want all of the brown bits to help flavor the gravy. Reserve around 1 tablespoon of the beef fat and drain off any excess
Reduce the heat to medium then add the sliced onions and mushrooms and cook for 5-6 minutes, stirring occasionally, until all of the liquids from the mushrooms have cooked off and they are lightly browned. Add the minced garlic and cook for around 30 to 45 seconds until fragrant, stirring constantly to avoid burning.
Add the butter and let melt, then add in the flour and cook for around 2 minutes, stirring frequently, until the flour is golden brown. Slowly add the beef stock while whisking. Continue whisking for about 45 seconds to avoid clumps and scrape up any brown bits on the bottom of the pan. Stir in the Worcestershire sauce and dried thyme.
Add the hamburger steaks back to the pan. Cover and cook for 5 to 10 minutes until the patties are cooked through and the gravy is thickened. Top with fresh chopped parsley before serving.