1.Make parsnip mash. Boil, steam or microwave potatoes and parsnip until tender, drain. Combine potatoes and parsnip with milk and butter in bowl, mash until smooth, stir in cheese, season to taste.
2.Preheat oven to 200°C (180°C fan forced).
3.Meanwhile, heat oil in large saucepan, add onion and chicken, cook, stirring, until browned. Add carrot and celery, cook, stirring, until soft. Stir in flour then gradually add stock, sauce and mushrooms, cook, stirring, until mixture boils and thickens. Stir in peas, season to taste.
4.Spoon mixture into 2.5-litre (10-cup) ovenproof dish, top with parsnip mash. Bake, uncovered, in oven, about 30 minutes or until browned and heated through.
This pie is suitable to freeze. Thaw in the fridge overnight before reheating.Note