Heat the oven to 200°F and arrange a rack in the middle. Cut the loaf of bread in half horizontally and open it up like a book. Spread the mayonnaise, if using, on the bottom piece of bread. Evenly place the ham and roasted pork on top of the mayonnaise. Evenly arrange the cheese and pickles on the meat.Spread the mustard on the top piece of bread and close the sandwich. Press gently on the top to compact the sandwich slightly. Cut it in half crosswise; set both halves aside.Lay 2 (20-inch-long) sheets of aluminum foil on a work surface. Brush half of the melted butter on the tops of the sandwiches. Place each sandwich butter-side down on the sheets of foil. Brush the bottoms of the sandwiches with the remaining butter. Fold the foil around the sandwiches to completely encase them.

Heat a large frying pan on low heat until hot, about 4 minutes. Place 1 wrapped sandwich in the pan. Place a cast-iron skillet, Dutch oven, or heavy pot on the sandwich, push down on the skillet or pot to further compact the cubano, and cook undisturbed for 10 minutes.

Remove the skillet or pot (careful: It may be hot). Flip the sandwich and place the skillet or pot back on top of it. Cook undisturbed until the cheese has melted and the sandwich is warmed through, about 10 minutes more. Remove to the oven and repeat with the second sandwich. When both are ready, remove the foil, cut into pieces, and serve