Mustard Horseradish Sauce:
1 1/2 cups good mayonnaise
3 tablespoons Dijon mustard
1 1/2 tablespoons whole-grain mustard
1 tablespoon prepared horseradish
1/3 cup sour cream
1/4 teaspoon kosher salt
Whisk together the mayonnaise, mustards, horseradish, sour cream, and salt in a small bowl.
SERVE THIS WITH STANDING RIB ROAST, CONTESSA