Fish pie with watercress sauce is a comforting and delicious dish that combines flaky fish, creamy mashed potatoes, and a vibrant watercress sauce. The fish is poached in a flavorful broth, then mixed with peas and topped with a layer of creamy mashed potatoes. The watercress sauce adds a fresh and peppery flavor to the dish, making it a perfect choice for a cozy dinner. This recipe is easy to make and can be enjoyed by the whole family.