Combine the olive oil, vinegar, prunes, olives, capers, bay leaves, garlic, oregano, thyme, salt and pepper in a large bowl. Add the pork and stir to coat. Cover the bowl or transfer contents to a big Ziploc bag and refrigerate for a couple of hours or overnight.
Heat the oven to 400 degrees.
Remove the pork and wipe it off, reserving the marinade. In a medium roasting pan, over medium heat, add a few tablespoons of olive oil and brown pork on all sides, for a few minutes total. Remove pork to a plate and add a couple of splashes of white wine to the pan to deglaze the tasty bits. Turn off heat.
Place the pork back in the pan. Pour marinade, olives and all, over the meat and add 1 cup of wine and enough of the chicken stock so the liquid reaches halfway up the sides of the meat. Sprinkle pork with the brown sugar.
Roast, basting once with the pan juices, until an instant read thermometer reads 140, 15 to 20 minutes. Remove to a cutting board. Let pork rest for 5 minutes.
Meanwhile, place the roasting pan over one or two burners on medium high and simmer to reduce the sauce a bit.
Slice the pork into medallions. (Great served over a puddle of soft polenta. Use instant polenta, but add twice the amount of liquid called for on the box: a mix of half milk, half water. After cooking, season with salt and whisk in several tablespoons of butter and a handful or two of freshly grated Parmesan.).
Spoon a good amount of polenta onto each plate and place medallions on top. Sauce the pork and pass the remaining juice in a gravy boat.