Hanger Steak with Mushrooms and Red Wine Sauce

Name: Hanger Steak with Mushrooms and Red Wine Sauce
Ingredients: 3 tablespoons extra-virgin olive oil, divided; 12 ounces assorted mushrooms, torn or cut into large pieces; Kosher salt, freshly ground pepper; 4 tablespoons (½ stick) unsalted butter, divided; 1 ½ pound hanger steak, trimmed, pounded to ½-inch thickness; Coarsely cracked black pepper; 3 garlic cloves, lightly crushed; 1 6-inch sprig rosemary; 1 cup dry red wine; ¾ cup low-salt chicken stock; 2 tablespoons chopped tarragon