Chicken and Leek Pie

olive oil
4 leeks, sliced
1 large onion, chopped
1 medium carrot, chopped
6-8 chats (baby potatoes), cubed
2 tbsp plain flour
6-8 boneless chicken thighs, cut into chunks
chicken stock
freshly ground salt & pepper
1 heaped tbsp freshly chopped parsley
2-3 sheets of frozen puff pastry
1 egg
¼ cup milk
Preheat oven to 190°C. Heat a little oil in a large pot and gently saute leeks, onion, carrot and potatoes. Add flour, turn heat down and gently cook for 2-3 mins, regularly stirring. Then add chicken pieces and stock to just cover, together with seasonings and parsley. Mix well, turn heat up, bring to the simmer and cook for about 20 mins until chicken and vegies are tender, adding more stock if needed. Transfer mixture into a large gratin (or ovenproof) dish and allow to cool. Then cut out rounds of pastry using pastry cutters (or a glass) and place on the pie, overlapping them a little. Whisk together egg and milk and brush over the pastry. Cook in oven for about 10-15 mins until risen and golden.