01 - Cook the beef bacon in a skillet over medium heat until crisp, about 5 to 7 minutes. Drain on paper towels.
02 - Lightly toast the sandwich bread slices. Optionally, spread a thin layer of butter on each slice for enhanced flavor.
03 - Spread mayonnaise evenly over one side of each slice of toasted bread. If using, add Dijon mustard alongside mayonnaise.
04 - Place one slice of bread, mayonnaise side up, on a plate. Layer with a romaine leaf, turkey slices, and a tomato slice. Season lightly with salt and freshly ground black pepper.
05 - Top with a second slice of bread, mayonnaise side down. Spread mayonnaise on the exposed top side, then layer with crisp beef bacon and red onion slices if desired.
06 - Add the final slice of bread, mayonnaise side down, to finish the sandwich.
07 - Press the sandwich gently, then cut into halves or quarters using a serrated knife. Secure portions with toothpicks if preferred and serve immediately.