In a large mixing bowl, combine the ground beef, panko breadcrumbs, egg, minced shallot, minced garlic, ketchup, Worcestershire sauce, Dijon mustard, onion powder, kosher salt, and a few cracks of pepper.

Gently mix by hand until the ingredients are well incorporated, being careful not to overmix.

Divide the meat mixture into 4 equal parts and shape each into an oval patty about ¾ inch thick.

Preheat a frying pan over medium-high heat for 1-2 minutes.

Add 2 tablespoons of butter to the hot pan and melt.

Place the steak patties in the pan and cook undisturbed for 4-6 minutes per side, until fully cooked.

Remove the steaks from the pan, leaving the grease and drippings behind, and set them aside on a plate.

Reduce the heat to medium-low. Add the remaining 1-2 tablespoons of butter to the pan and melt, ensuring there are about 3-4 tablespoons of grease.

Add the sliced baby bella mushrooms and cook, stirring occasionally, for 2-3 minutes until they begin to brown and turn tender.

Stir in the sliced garlic and sliced shallot, cooking for another 2 minutes while stirring often to prevent burning.

Sprinkle the vegetable mixture with flour, stirring to fully combine.

While whisking, slowly pour in 1 cup of beef broth, followed by the dry white wine. Stir for 15-20 seconds until the flour is fully incorporated with no clumps remaining.

Add the remaining beef broth, water, ketchup, Dijon mustard, Worcestershire sauce, and salt and pepper to taste. Stir until well combined.

Simmer the gravy for 3-4 minutes, stirring occasionally, until it begins to thicken.

Return the Salisbury steaks and any collected juices back to the pan, spooning some gravy over each steak.

Continue simmering for another 3-4 minutes, stirring the gravy around the steaks, until the steaks are warmed through and the gravy has thickened.

Remove from heat, garnish with chopped parsley, and serve the steaks with mashed potatoes.