Adjust oven rack to lower-middle position and preheat oven to 325°F. Coat a large Dutch oven with olive oil and bring to high heat. Season meat with salt and pepper. Working in batches to avoid overcrowding, add short ribs and cook without moving until well browned on first side, about 4 minutes. Flip short ribs and add onions and garlic. Continue cooking, stirring occasionally, until short ribs are browned on second side and onions and garlic are softened but not completely browned, 2 to 3 minutes longer.

Add red wine to pan. Bring to a boil and let it simmer for a minute before adding beef broth, Worcestershire, vinegar, brown sugar, bay leaves, and orange zest. Return to a boil, cover, and transfer to the oven to cook until meat is fork-tender and sauce is rich and full of depth, 2½ to 3 hours total, flipping meat once during cooking.

When short ribs are done cooking, discard bay leaves and orange zest. Season salt to taste with salt and pepper. To plate, place a mound of mashed potatoes on each of four individual plates. Top with a short rib, and spoon with sauce. Serve immediately.