Heat oven to 325°F. In small bowl, combine bread crumbs, parsley, horseradish, and 1/2 teaspoon salt.
Sprinkle remaining salt over beef. Spread sour cream on top, and cover with bread crumbs. Place in roasting pan, and cook 75 minutes, or until meat thermometer reads 135°F. Let stand 15 minutes (temperature will rise to 145°F for medium rare).
To make bread crumbs, place 2 slices of firm white bread in food processor fitted with chopping blade. Pulse until chunky bread crumbs form.