This recipe does make quite a bit, so I would recommend starting with a half batch unless you're having a huge party!
White Barbecue Sauce
1 1/4 cups light mayonnaise
1/4 cup horseradish (I upped this to about 1/3 cup)
3 tbsp cider vinegar
juice of 2 lemons (I only used the juice of one and would use less next time)
salt and pepper to taste
Combine all ingredients and refrigerate for at least one hour before serving.
from Macaroni and Cheesecake, originally from Southern Living