Remove the silver skin from the tenderloin: slip a paring knife between the silver skin and the muscle fibers. Angle the knife slightly upward and use a gentle back-and-forth sawing action.
Slice the tenderloin into 1"-thick slices. Smack each slice with the flat of your chef's knife once or twice, to flatten them to about 3/4" thick. Sprinkle salt and pepper over both sides of pork slices.
Heat oil until shimmering in heavy-bottomed pan, at least 10 inches across bottom, over medium-high heat, swirling pan to distribute oil. Working in batches of no more than six slices to avoid overcrowding, sear medallions without moving them until brown on one side, about 80 seconds (oil should sizzle, but not smoke). Turn medallions with tongs to avoid scraping off the sear; sear until meat is mostly opaque at sides, firm to the touch, and well browned, about 80 seconds. Transfer pork to plate.
Mix cinnamon, cloves, cayenne and brown sugar in small bowl; set aside. Heat oil in pan in which pork was cooked over medium heat, swirling to distribute. Add onion; sauté until softened and starting to color, about 2 minutes. Add spice mixture, sherry, and vinegar; boil, scraping pan bottom with wooden spatula to loosen browned bits, until liquid reduces to a glaze, about 2 1/2 minutes. Increase heat to high and add broth, raisins, and any accumulated pork juices; boil until liquid reaches consistency of maple syrup, about 3 minutes.
Reduce heat to medium; return pork to pan, turning meat to coat. Simmer to heat pork thoroughly and blend flavors, about 3 minutes. Adjust seasonings, adding salt to taste. Transfer pork to serving plate and spoon sauce over meat. Serve immediately.