1/3 cup red wine
1/3 cup soy sauce
2 tablespoons light brown sugar
2 lbs. pork tenderloin
1/3 cup mayonaisse
1/3 cup sour cream
1 1/2 tablespoons mustard powder
1 tablespoon minced chives
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 mayo, sour cream and mustard powder; mix well. Mix in minced chives. Chill until ready to serve.
Preheat oven to 325 degrees F. Place meat and marinade in shallow baking dish, and roast for 1 hour, basting occasionally. Tempreture of meat should register 145 degrees F. Let rest for a few minutes, then cut into 1/2 inch thick slices. Serve with mustard sauce.