How to Make It
Set the pork on a work surface, fat side down. To butterfly the meat, make a lengthwise cut in the pork from end to end, cutting two-thirds of the way through the meat. Make a 1/2-inch-deep lengthwise cut in each side of the first cut, so the roast lies flat. Season the pork all over with salt and pepper.
In a large shallow baking dish, combine the wine, garlic and pork, turning to coat. Let marinate at room temperature for 1 hour, turning the meat once.
Preheat the oven to 450°. Remove the pork from the dish and scrape off the garlic. Strain the wine and reserve 1/2 cup. Lay the pork on a work surface, cut side up, and season with salt and pepper. Arrange the whole prunes down the length of 1 of the side cuts. Repeat with the whole apricots along the other side cut. Roll up the roast to reshape it and tie at even intervals with cotton string.
Set the pork in a small flameproof roasting pan and season with salt and pepper. Roast in the upper third of the oven for 15 minutes. Baste with the pan juices, reduce the oven temperature to 400° and roast for about 30 minutes, or until an instant-read thermometer registers 150° for rosy meat. Transfer the roast to a cutting board, cover loosely with foil and let stand for 10 minutes.
Meanwhile, whisk the flour into the pan juices to form a smooth paste. Gradually whisk in the reserved 1/2 cup of wine until smooth. Set the roasting pan over 2 burners on low heat and whisk in the stock. Add the quartered prunes and apricots and simmer, stirring often, until the sauce is flavorful, about 10 minutes.
Add any accumulated juices from the roast to the sauce and whisk in the mustard. Season with salt and pepper and pour into a warmed gravy boat. Carve the pork into 1/3-inch-thick slices and serve at once with the sauce.