Peel and cut potatoes into 2.5cm chunks and boil in chicken stock.
Meanwhile, melt butter then fry diced onion and sliced leek until translucent. Dice bacon and fry with onion and leek. Combine leek mixture with potatoes and add salt, pepper, mustard and parsley to taste. Cook for about 1/2 hour until potatoes start to be absorbed into the soup.
Take off heat and rest for 1/2 hour. Cut up smoked sausage and add to soup with milk and reheat slowly. Serve with crusty bread.
If you do not have smoked Dutch sausage, you can use any sausage you like, as long is it is pre-cooked.