01 - Heat a skillet over medium heat and cook the beef bacon slices until crisp, about 5–7 minutes. Drain on paper towels.
02 - Lightly toast all bread slices. Optionally, spread a thin layer of butter on each slice for enhanced flavor.
03 - Spread mayonnaise evenly over one side of each toasted bread slice. If using, add Dijon mustard on top of the mayonnaise.
04 - Place one slice of bread mayo side up on a plate. Layer with a romaine leaf, roasted turkey slices, and a slice of tomato. Lightly season with salt and pepper.
05 - Top with a second bread slice, mayo side down. Spread mayonnaise on the top side of this slice. Add crispy beef bacon and red onion slices if desired.
06 - Complete with the final bread slice, mayo side down. Press gently to compact the sandwich.
07 - Cut the sandwich into halves or quarters using a serrated knife. Secure portions with toothpicks if preferred. Serve immediately.