Part 1: Forming the Salisbury Steak Patties

1. Prepare the Onion: Using the large holes of a box grater, grate the small yellow onion into a large mixing bowl. This technique releases the onion’s juices and creates a very fine texture. Alternatively, you can mince it as finely as possible.
2. Combine the Ingredients: To the bowl with the grated onion, add the ground beef, Panko breadcrumbs, beaten eggs, ketchup, 2 tablespoons of Worcestershire sauce, garlic powder, salt, and pepper.
3. Mix Gently: Using your hands, gently mix all the ingredients together until they are just combined. Be careful not to overmix! Overworking the meat will result in tough, dense patties. Mix only until you no longer see streaks of individual ingredients.
4. Form the Patties: Divide the meat mixture into 6 equal portions. Gently shape each portion into an oval-shaped patty, about 3/4-inch to 1-inch thick. The oval shape is traditional for Salisbury Steak. Place the formed patties on a plate or baking sheet.

Part 2: Searing the Patties for Maximum Flavor

1. Heat the Skillet: Place your large skillet over medium-high heat. Add the 2 tablespoons of olive oil.
2. Sear the Patties: Once the oil is hot and shimmering, carefully place the patties in the skillet. You may need to do this in two batches to avoid overcrowding the pan. Cook the patties for 3-4 minutes per side, until a deep, dark brown crust has formed. The goal here is not to cook them through, but to develop flavor.
3. Set Aside: Once seared, transfer the patties to a clean plate. They will finish cooking later in the gravy. Do not wipe out the skillet! The browned bits (called “fond”) left in the bottom of the pan are pure flavor and the foundation for your gravy.

Part 3: Making the Rich Onion Gravy and Finishing the Dish

1. Sauté the Onions and Mushrooms: Reduce the heat to medium. Add the 4 tablespoons of butter to the same skillet. Once melted, add the thinly sliced onions and the sliced mushrooms (if using). Sauté, stirring occasionally, for 8-10 minutes, until the onions are soft, translucent, and starting to caramelize. Use your spoon to scrape up some of the browned bits from the bottom of the pan as you stir.
2. Create the Roux: Sprinkle the 4 tablespoons of all-purpose flour over the cooked onions and mushrooms. Stir constantly and cook for about 1-2 minutes. This step cooks out the raw flour taste and creates the roux, which will thicken the gravy.
3. Build the Gravy: While stirring or whisking continuously, slowly pour in the 4 cups of beef broth. Pouring slowly while whisking is crucial to prevent lumps from forming.
4. Season the Gravy: Once all the broth is incorporated, stir in the 1 tablespoon of Worcestershire sauce and 1 teaspoon of Dijon mustard. Bring the mixture to a simmer. As it simmers, continue to scrape the bottom of the pan to release all of the remaining flavorful fond.
5. Simmer and Thicken: Let the gravy simmer for about 5 minutes, stirring occasionally, until it has thickened slightly. Taste the gravy and season with salt and pepper as needed.
6. Return the Steaks to the Pan: Gently place the seared Salisbury Steak patties back into the simmering gravy. Spoon some of the gravy and onions over the top of each patty.
7. Finish Cooking: Reduce the heat to low, cover the skillet, and let the steaks simmer gently in the gravy for 10-15 minutes, or until they are cooked through and tender.
8. Serve: Garnish with fresh chopped parsley and serve immediately.