This classic southern barbecue sauce is used as a condiment for grilled food rather than an on-grill flavoring. Easy to make, we use ours on everything from pulled pork sandwiches to roasted potatoes or grilled veggies. Whole grain mustard adds texture and bite to the creamy mayonnaise, which is made piquant by the addition of both garlic and horseradish. It’s most delicious on barbecued chicken, and we particularly like to brush finished chicken kebabs with this sauce. You can make this sauce ahead and keep in the refrigerator for up to two weeks.