Whisk the horseradish, mustard, garlic, olive oil and 2 tablespoons pepper in a bowl.
Spread generously over the beef.
Marinate, covered, in the refrigerator for 1 to 2 hours.
Season with kosher salt and additional pepper.
Grill or broil to desired temperature.
Note: It is best never to pierce a steak with a fork when turning as you will lose some of the juices and cause the steak to be less tender.
Also, when grilling, may I suggest grilling an onion at the same time (This trick taught to me by Titanium Chef, her recipe#25572).
Note: To avoid the crust from falling off while grilling I suggest using a flat grill pan (the type with the holes in it). Be sure to spray it with a non-stick spray and let it heat before placing the steak on it.