Chef Judi's recipe is Prime Rib of Beef with Horseradish Cream Sauce
½ cup, plus 2 TBSP -- sour cream
1½ TBSP -- prepared white horseradish, drained
1½ TBSP -- green peppercorns, drained and minced
Whisk sour cream in a bowl, pour in horseradish and peppercorns, season and add more horseradish if needed. Can be made up to 24 hours ahead.