Ingredients:-

For beef:-
1. Fillet of beef, trimmed and tied (2to3pound)
2. Kosher salt (2tsp)
3. Dijon mustard (1tsp)
4. coarsely ground black pepper (2tsp)
5. unsalted butter (1tbsp)

For sandwich:-
1. 7 grain bread
2. arugula (1bunch)
3. Kosher salt (to taste)
4. freshly ground pepper (to taste)
5. mustard horseradish sauce (1/2 tsp)
6. unsalted butter at room temperature
7. good mayonnaise (3/4c)
8. sour cream (2tbsp)

Method of preparation:-
1. First heat the oven to 500 degrees F. Take a baking sheet, place beef on it and then pat it with paper towel to dry it. , take a small bowl, mix butter and mustard in it.

2. Mix this mixture over the beef with hands and then sprinkle salt and pepper over it. Now place this in oven to roast it for about 22 to 25 minutes for rare or medium heat.

3. Now take out the beef from the oven. Cover it and keep it for about 20 minutes at room temperature. Cut the roasted beef into slices after 20 minutes.

4. To make sandwich, take bread and cut it into ¼ inch slices. Take a bowl, mix mayonnaise, horseradish, sour cream, a pinch of salt. Mix these well to make 1 cup of mustard horseradish sauce.

5. Spread mustard horseradish sauce over the slice, and then place slices of beef, arugula and then sprinkle salt and pepper according to taste.

6. Spread butter on 4 slices of bread and place it with butter side down on the top of the beef slices. Now the beef and horseradish sauce sandwich gets ready.