Peel and finely chop the onion. Cut the smoked pork into cubes as well. Heat the fat in a large pot. Stir-fry the sausage and onions in it. Deglaze with broth, bring to the boil and add the frozen vegetables.
Cover and cook for about 10 minutes. Let the mashed potatoes trickle into the hot soup while stirring carefully. Bring to the boil again briefly and season to taste with salt, pepper and possibly some Worcester sauce.
Wash parsley, dab dry and cut into fine strips. Serve the soup sprinkled with parsley.