In a large bowl, mix the ground beef, breadcrumbs, egg, Worcestershire sauce, ketchup, garlic powder, onion powder, salt, and black pepper. Combine until just mixed, then form the mixture into 4–6 oval-shaped patties.

Heat a large skillet over medium-high heat. Add a splash of oil and sear the patties for 3–4 minutes per side until browned. Remove from the skillet and set aside.

In the same skillet, melt butter over medium heat. Add onions and mushrooms, sautéing for about 5 minutes until softened.

Sprinkle flour over the onions and mushrooms and stir to coat. Cook for 1–2 minutes to remove the raw flour taste.

Gradually whisk in beef broth, Worcestershire sauce, Dijon mustard, salt, and pepper. Bring to a simmer.

Return the patties to the skillet, nestling them into the gravy. Cover and cook over low heat for 10–15 minutes, allowing the patties to cook through and the gravy to thicken.

Serve the Salisbury steaks hot, spooning the gravy over them. Pair with mashed potatoes, rice, or egg noodles.