Prepare the White Barbecue Sauce by combining mayonnaise, vinegar, mustard, sugar, garlic, and horseradish in a mixing bowl until smooth.

Marinate the chicken in the sauce for at least 4 hours or overnight by placing it in a zip-lock bag with the sauce and refrigerating.

Preheat the grill to high heat (450°F to 500°F) and ensure the grates are clean and oiled.

Remove chicken from marinade, rinse, and pat dry. Coat with olive oil, seasoning generously with salt and pepper.

Grill chicken skin-side down for 2-3 minutes until golden, then flip and grill the other side for an additional 2 minutes.

Move chicken to cooler side of the grill, skin-side up, and lower heat to medium (425°F). Cover and cook for about 5 minutes.

Baste the chicken with reserved White Barbecue Sauce after 5 minutes, repeating every 5 minutes for caramelization.

Grill for an additional 10-20 minutes until internal temperature reaches 160-162°F.

Let the chicken rest for about 5 minutes before serving.

Serve with extra White Barbecue Sauce on the side.