In a medium bowl, mix all of the steak ingredients except the oil together until well combined combined.
Shape the meat mixture evenly into 4 oval patties, about ¾-inch thick.
Heat the oil in a large skillet over medium-high heat. Add the patties and cook until well browned on each side, about 3 minutes per side. Remove from skillet and set aside.
For the Gravy:
Add the butter to the same skillet and melt over medium heat. Add the onion, mushrooms, and garlic. Cook, stirring frequently, until the onion is softened, about 5 minutes. Add the flour and stir constantly for 1 minute.
Gradually stir in the stock. Stir in the Worcestershire sauce, salt, and pepper. Bring to a boil, then reduce the heat to low.
Return the patties to the skillet, nestling them among the gravy. Cook until the patties are cooked through and the gravy has thickened, about 5 to 7 minutes. Serve garnished with chopped parsley.
Notes
Avoid overmixing the meat. Beat the egg first to help it easily incorporate, then gently mix the ground beef and seasonings until just combined to avoid tough or dense meat patties.
Shape patties evenly. Form the patties into uniform ¾-inch thick oval shapes to ensure they cook evenly and at the same rate.
Sear to lock in flavor. Searing the patties over medium-high heat in the skillet develops a flavorful crust before simmering in the gravy. This helps lock in the juices and adds depth of flavor to the final dish.
Adjust gravy consistency. If your gravy seems thin, thicken it by simmering for longer after adding the beef stock. If needed, you can also mix a small amount of cornstarch with water and add it to the gravy while simmering to thicken it.
Don’t crowd the skillet. If needed, cook the patties in batches to avoid overcrowding, which can lead to steaming rather than searing.
Adjust seasonings to taste. Once the gravy has thickened, taste it and add more seasonings to taste as needed to suit your preferences.