These sandwiches originated in New York City and are traditionally made on a flat top grill; however, most people do not have those so I created a cast iron skillet version.
Step: 1
Combine mustard, ketchup, and cherry peppers in the bowl of a food processor. Pulse until smooth and set aside.
Step: 2
Melt butter in a small skillet over medium-high heat. Add onions and cook until onions are soft and are starting to caramelize, about 5 minutes. Remove from heat and set aside.
Step: 3
Form beef into two patties and season with salt and pepper. Heat a large cast iron skillet over medium-high heat. Add hamburger patties and cook 5 minutes or until a crust forms on the bottom. Flip patties over and cook 3 minutes.
Step: 4
Using a wide spatula, break patties up into large pieces. Sprinkle sauteed onion in between the spaces of the hamburger pieces. Layer cheese over the beef, and cook 2 minutes or until cheese is melted.
Step: 5
Spread reserved mustard sauce on the bottom bun of each hoagie roll. Divide meat mixture between the two sandwiches. Top each with shredded lettuce and sliced tomato.
Per Serving: 804 calories; protein 51.2g; carbohydrates 46.6g; fat 44.8g; cholesterol 173.4mg; sodium 1775.8mg.