Filet of Beef with Mustard Horseradish Sauce

Name: Filet of Beef with Mustard Horseradish Sauce
Yield: 8-10
Ingredients: 1 Filet of beef (4 to 5 pounds), whole; 1 Parsley, Fresh; 3 tbsp Dijon mustard; 1 tbsp Horseradish, prepared; 1 1/2 cups Mayonnaise, good; 1 1/2 tbsp Mustard, whole-grain; 1 Mustard horseradish sauce; 1 tbsp Black pepper, coarsely ground; 1 1/8 tbsp Kosher salt; 2 tbsp Butter, unsalted; 1/3 cup Sour cream