I found this recipe many years ago in a Cooking Light magazine, and this is really a winner!! The Blackberry Mustard makes 16 servings, so I freeze the leftover in 1/4 cup servings, and can defrost one or two whenever I fix a grilled meat and am hungry for the sauce. This recipe maybe looks putsy, but I make it lot for company since I can brown it and let it cook for 30 minutes, then finish it off. Everybody always gathers in the kitchen anyway, so I usually put one or two of the guests to work to help finish the meal. The dry rub on the tenderloins makes the blackberry mustard sauce taste even sweeter. I have used both fresh and frozen blackberries in this recipe and both taste great!!