Step 1

Heat butter and oil in a large frypan over medium-low heat. Cook leeks, stirring, for 10 minutes until soft and wilted.

Step 2

Meanwhile, cook potato in boiling salted water for 5 minutes. Drain well. Add to frypan with chicken and cook, stirring, for 5 minutes. Add ham, cream and mustard. Cook for a further 5 minutes, stirring. Add parsley, season and cool completely.

Step 3

Preheat oven to 180°C. Lightly grease a 25cm loose-bottomed tart pan. Line base and sides with shortcrust pastry. Chill for 15 minutes. Line with baking paper and pastry weights or uncooked rice. Bake for 10 minutes. Remove paper and weights and bake for 5 minutes until golden. Add filling. Top with puff pastry and press edge with tines of a fork to seal. Brush with egg. Prick pastry a few times with a fork. Chill and cook later or bake for 25 minutes until golden. Serve hot or warm with salad.