Bobby Flay’s Salisbury Steak with Mushroom Gravy Serves: 4 Prep Cook Time: ~40 minutes  Ingredients For the steaks: • 1 lb ground chuck • 1 egg, lightly beaten • 2 tablespoons grated Parmesan cheese • 2 tablespoons breadcrumbs • 1 teaspoon garlic, crushed into a paste • Kosher salt & freshly ground black pepper • 2 tablespoons canola oil  For the mushroom gravy: • 1 dozen cremini (button) mushrooms, stemmed and quartered • ½ white onion, thinly sliced • 1 tablespoon tomato paste • 1 teaspoon W