There are times when you feel like having a sandwich, and nothing less than a thick, juicy steak sandwich will do! Well, this is the recipe for those occasions! I always look forward to the hearty beef flavor and firm texture of top sirloin, and I recommend USDA prime grade and well-trimmed center cuts. Pounding the steaks lightly with a meat mallet or rolling pin not only makes them easier to eat but helps tenderize them. The technique of slowly caramelizing onions accentuates their natural sweet light tones and gives them a depth of flavor. You can use sweet onions (such as Vidalia or Maui) if you want an almost syrupy topping for the steaks. Using the smaller, more tender inner romaine leaves for the sandwich, and fresh vine-ripened tomatoes if possible. If you like smoky flavors, a good-quality smoked cheese will complement and highlight the grilled flavor of the steaks, especially of you use soaked mesquite or hickory wood chips on the grill.
