Roast Beef and Horseradish Sandwich

Instructions

1. Prepare the horseradish cream
   In a small bowl, combine the sour cream, horseradish, Dijon mustard, and lemon juice. Mix well until smooth and creamy. Season with salt and pepper to taste.
2. Toast the bread (optional)
   If desired, lightly butter the bread slices on one side and toast them in a skillet over medium heat until golden brown, about 2 minutes per side. Allow to cool slightly before assembling.
3. Assemble the sandwich base
   Spread a generous layer of the horseradish cream on one side of each bread slice. On four of the slices, arrange a layer of arugula leaves, followed by the thinly sliced red onion.
4. Add the roast beef
   Divide the roast beef evenly among the four sandwiches, layering it on top of the onions. Season lightly with freshly ground black pepper.
5. Complete the sandwiches
   Add sliced tomatoes on top of the roast beef. Place the remaining bread slices on top, horseradish cream side down, and press gently to secure the sandwich.
6. Slice and serve
   Using a sharp knife, cut each sandwich diagonally and serve immediately. For a more elegant presentation, you can remove the crusts before cutting.