Preheat oven to 200°C.
Gently fry the leeks and onion in a pan over low heat with olive oil and garlic, until softened (about 5 minutes). Add the mushrooms and thyme and fry for another 5 minutes. Add a splash of white wine and fry off for a minute or two, before adding chicken stock and salt and pepper to taste.
Shred the chicken meat into the sauce and cook for 10 minutes. Add cream and simmer for another 15 minutes. Stir in the flour paste to thicken the filling and simmer for a further 10 minutes. Remove from the heat.
Spoon the filling into four small ovenproof dishes or one large dish.
Unroll the puff pastry on a lightly floured surface and use a rolling pin to stretch it out to fit the top of the chicken filling. Carefully place over the dishes and press down to secure, cutting away any excess pastry. Brush with the beaten egg to coat the surface of the pastry.
Bake for 15-20 minutes until puffed up and golden.
For perfect gravy: It’s essential to have enough gravy in a chicken pie so the chicken is succulent and tender after slow cooking – but too much liquid will make your pastry crust soggy. To make the perfect gravy using the pan juices, stock and cream, add a thickener to bring it all together. Making a flour paste is better than sprinkling maize flour or flour straight into the filling, as the paste dissolves quickly and easily and you aren’t left with an uncooked flour taste.
Recipe by Hannah Lewry. First published in City Press.