Clean the fish and pat dry. Sprinkle salt and white pepper on both sides and marinate for 20 minutes.
Cut the tomatoes. Peel the potato and cut into desired size. Place in water and bring to a boil.
Take the fish out. Pat dry once again if there is excess water. Sprinkle cornstarch on both sides. Heat the oil and sauté the ginger slices on high-medium heat. Put the fish in and turn to low heat and fry on both sides.
Pour a bowl of tomato and potato soup in. Cook with the fish until the soup has a milky colour.
Pour the fish and the soup back into the pot with tomato and potato soup. Bring to a boil on high heat. Turn to low heat and simmer for 1 hour.