Roast Beef and Cheddar Sandwich

Instructions

1. Prepare the spread
   In a small bowl, combine the mayonnaise, horseradish sauce, and Dijon mustard. Mix well until smooth and set aside.
2. Toast the bread
   Heat a large skillet or griddle over medium heat. Butter the outside of each bread slice. Place the bread buttered-side down on the hot surface and toast until golden brown, about 2-3 minutes.
3. Assemble the base
   Spread the horseradish-mayo mixture on the untoasted sides of the bread. Layer the bottom slice with arugula leaves, followed by sliced red onions and tomato slices.
4. Add the main fillings
   Arrange the thinly sliced roast beef evenly over the vegetables. Make sure to fold or loosely stack the beef for better texture and easier eating.
5. Add cheese and finish
   Place the cheddar cheese slices over the roast beef. If desired, return the open-faced sandwich to the skillet for 30 seconds to slightly melt the cheese. Top with the second slice of toasted bread, toasted side up, and press gently.
6. Slice and serve
   Using a sharp knife, cut the sandwich diagonally and serve immediately with pickles and potato chips on the side if desired.