In a large bowl, mix the ground beef, breadcrumbs, onion, garlic, ketchup, Worcestershire, mustard powder, parsley, egg and salt and pepper until just combined. Try not to overmix!
Form the meat into 6 patties. To make them as even as possible for cooking purposes, divide the meat into two. Then divide each of those pieces into three equal sized patties.
In a large skillet, melt the butter and heat over medium-high heat until sizzling. Place the meat patties into the pan and cook the patties until browned on both sides. This is where they get that good "crust", so don't skip the butter, and make sure you really brown and crisp them up!
Pull the patties out and set aside on a plate. Tent with foil to keep warm. These are not fully cooked and will be cooked until finished at the end.
Drain all but one tablespoon of the ground beef fat out, leaving the brown bits for flavor.
For the gravy, melt the next amount of butter in the skillet add the mushrooms and onion and cook until onion is translucent. Sprinkle the flour over the onions and stir into the mixture.
Add a bit of the beef broth slowly, scraping the bottom of the pan to deglaze all the brown bits. Once done, add the rest to the skillet stirring continuously.
Add ketchup and the Worcestershire sauce TO TASTE (start with one tablespoon), then add sherry if desired then stir, bring to a boil then reduce heat and place the beef patties back into the pan.
Cook until the sauce has thickened and the patties are cooked all the way through, to at least 165 °F.
Serve immediately over mashed potatoes or rice, with fresh parsley as garnish.
Worcestershire sauce can be overpowering for some people, start low and add to taste.
Cooking sherry adds a classic and traditional sweetness to this dish if you want!
All calories and info are based on a third party calculator and are an estimate. Actual nutritional info will vary with brands used, your measuring methods etc.