Soak the lentils in cold water for approximately 2 hours.
Roughly chop 2 celery stalks, 2 carrots and 1 red onion. Place in a large pot with the pork hock, half of the Winter Soup Mix and cover with the water. Add a pinch teaspoon of salt and bring to the boil. Simmer gently for 2 hours or until the pork is tender. Remove the pork hock and set aside. Strain the stock, discarding the solids.
Finely chop the remaining vegetables. Heat olive oil in a pot, add chopped vegetable and sauté with the remaining Winter Soup Mix and a pinch of salt until soft, then add the strained pork stock. Bring to a simmer, then add the drained lentils. Cook for 15-20 minutes, until the lentils and potatoes are both tender. Roughly shred the pork hock and stir through the soup.
Toss the cavolo nero and lemon juice together in a bowl with a pinch of salt and rub together with your hands until it begins to wilt – about 2 minutes. Divide the kale amongst your serving bowls and ladle the hot soup over the top.
Sprinkle with parsley and celery leaves and serve with grilled crusty bread.