FOR THE BURGERS: 1 tablespoon olive oil 1 medium sweet onion, finely diced (about ⅔ cup) Salt and freshly ground black pepper 2 garlic cloves, minced 3 pounds freshly ground beef chuck (preferably prime grade) 4 tablespoons finely chopped fresh Italian parsley ⅓ cup sun-dried tomatoes 1 cup bread crumbs 2 teaspoons Dijon mustard 2 teaspoons Worcestershire sauce ½ teaspoon salt ¼ teaspoon freshly ground black pepper 2 large eggs, beaten to blend 4 3½-inch squares ciabatta bread, halved horizontally 2 tablespoons butter, room temperature FOR THE GOURMET KETCHUP: ½ cup ketchup 1 tablespoon Dijon mustard 1 tablespoon Sherry vinegar 1 tablespoon Worcestershire sauce 1 tablespoon finely chopped fresh chives 2 teaspoons finely chopped fresh tarragon 3 tablespoons extra-virgin olive oil

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