Combine wine, soy sauce, and brown sugar in a large resealable plastic bag.
Place tenderloin in bag, and refrigerate overnight, or at least 8 hours.
In a small bowl, combine mayonnaise, sour cream, mustard powder; mix well.
Mix in minced chives if you wish. Chill until ready to serve.
Preheat oven to 325 degrees F (165 degrees C).
Place meat and marinade in a shallow baking dish, and roast for 1 hour, basting occasionally. Temperature of meat should register 145 degrees F (63 degrees C).
Let rest for a few minutes, then cut into 1/2 inch thick slices.
