1. Heat the oil in a large frying pan over a medium heat. Add the onion and leeks and cook for 4-5 minutes until softened.

2. Add the chicken pieces and cook, stirring, for another 4-5 minutes. Stir in the garlic, add the wine and bubble away until reduced by two-thirds. Pour in the stock and simmer until reduced by half. Add the cream and tarragon, bring to the boil, then simmer for 5-6 minutes until thickened. Season, then spoon into a 2.5-litre pie dish (or 4 x 300ml ovenproof dishes). Set aside to cool.

3. Brush a little water along the edge of the pie dish or dishes. Unroll the pastry and cut out a piece large enough to cover the dish or dishes. Press down the edges and trim off the excess. Snip a small hole in the centre of the pastry to let the steam escape. Put on a baking tray and chill for 15 minutes.

4. Meanwhile, preheat the oven to 220C/fan200C/gas 7.

Beat the egg with a little salt, then brush over the pastry. Bake for 40-45 minutes (20-25 minutes if you are making individual pies) until the pastry is golden.