Pre-heat the oven to 220C/gas mark 7. Heat the oil in a large frying pan over a medium heat. Peel and finely chop the onion. Wash, trim and thickly slice the leeks. Add the onion and leeks and cook for 4-5 minutes until softened.

Cut the chicken into bite sized pieces and add to the onions and leeks, stirring for another 4-5 minutes. Crush and stir in the garlic, add the wine (if using) and simmer until reduced by two thirds. Make the chicken stock then pour in to the pan and simmer until reduced by half. Add cream, and roughly chopped tarragon, boil then simmer for 5-6 minutes until thickened. Spoon into a pie dish and cool.

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

Beat the egg and brush over the pastry. Bake for 40-45 minutes until the pastry is golden. Shred the cabbage leaves, place in a large saucepan and cover halfway with water. Bring to the boil and cook for 3-5 mins or until tender. Drain and discard the water.