To make the pork, preheat the oven to 450°F. 

Bore a hole lengthwise in the center of the roast: Start with a knife and then use a wooden spoon handle wrapped in plastic wrap; usually it is easier to work from both ends. The hole should be about as large as a nickel. Stuff with the dried prunes. Season the outside of the pork with salt and pepper.

In a roasting pan over medium-high heat, warm the olive oil. Add the pork and brown for 3 to 4 minutes per side. Add the carrots, celery, onion, rosemary, sage and garlic to the pan. Transfer to the oven and roast until an instant-read thermometer inserted into the center of the meat registers 150°F, about 40 minutes. Transfer the pork to a carving board, cover loosely with aluminum foil and let rest for 15 minutes.  

Set the roasting pan over medium-high heat and pour in the wine. Simmer until reduced by half. Add the stock and simmer until reduced by half again. Strain out the solids, return the liquid to the pan and stir in the butter to finish the jus. Adjust the seasoning with salt and pepper.

Make the potato fritters while the pork is roasting: Grate the potatoes into a bowl, add the egg and season with salt and pepper. Stir to combine.

In a large fry pan over medium-high heat, warm the peanut oil. Use 1/3 cup of the potato mixture for each fritter and form into disks about 3 inches in diameter. Add to the pan and cook for 5 minutes, then add the butter and cook for 5 minutes more. Carefully flip the fritters over and cook for 10 minutes more.

To serve, cut the pork into 1/2-inch slices. Place a fritter on each plate, top with the pork and spoon a little jus over all.