Salisbury Steak With Herby Mushroom Sauce

Name: Salisbury Steak With Herby Mushroom Sauce
Ingredients: Steaks:; 1 pound ground beef; 1/2 cup Panko breadcrumbs; 2 garlic cloves, grated or minced; 1 medium shallot, grated or minced; 1 large egg, beaten; 1/4 cup finely chopped parsley; 1 tablespoon Dijon mustard; 1 tablespoon dried oregano; 1 tablespoon dark brown sugar; 1 teaspoon Worcestershire sauce; 1/4 teaspoon cayenne; 1 teaspoon kosher salt; Freshly ground black pepper; Gravy:; 4 tablespoons olive oil, divided; 8 ounces mixed mushrooms (such as cremini, oyster, or shiitake), stemmed and sliced; 1 medium shallot, finely chopped or grated; 2 garlic cloves, minced; 2 tablespoons unsalted butter; 2 tablespoons all-purpose flour; 1/4 cup dry white wine; 2 cups unsalted beef broth; 2 tablespoons capers in brine, rinsed and dried; 1 1/2 teaspoons Worcestershire sauce; 1 teaspoon apple cider vinegar; 1 teaspoon dark brown sugar; Kosher salt, to taste; Fresh parsley, for serving; Fresh chives, for serving