Chicken and Mushroom pie with buttery mashed potatoes

Potato, Marinated cooked chicken breast with added water (15%) (chicken, water, cornflour), Milk, Mushroom (8%), Double cream (milk), White wine, Butter (milk), Onion, Wheat flour (wheat flour, calcium carbonate, iron, niacin, thiamin), Cornflour, Vegetable oils (rapeseed, palm, sunflower), Extra mature Cheddar cheese (milk), Chicken stock (water, yeast extract, chicken extract, salt), Salt, Porcini mushroom powder, White pepper, Yeast, Colours (plain caramel, paprika extract), Turmeric extract.