Heat the oil over a medium low heat in a large pot.
Add the Onions and brown for 5- 7 minutes until dark amber.
Stir in the garlic and ginger and saute for 2 minutes.
Add the chicken legs, thyme, leeks, chilli, stock, salt.
Bring to the boil and simmer on low for 40 minutes.
Strain the stock into a small pot.
Discard the thyme sprigs. Pour the stock back into the pot, then slowly pour in the cornflour mix. Return the pot to the heat and bring to the boil, stirring until thickened.
Remove from the heat and slowly stir in the yoghurt, mustard, chopped tarragon and pepper.
Shred the meat from the chicken bones and discard the bones.
Add the chicken to the stock and remove from the heat.
Preheat the oven to Gas Mark 6, 200 degrees C/Fan 180 degrees C
Melt the butter in a small pan and use a little to grease a round 20cm cake tin.
Line the tin with 4 layers of filo and butter the layers as you layer them.
Spread the chicken mixture in top. Fold the edges of the oil over the top and cover with 4 more layers of pastry buttering each layer as you go.
Brush the top of the pie with the egg mixture.
Bake in the oven for 30 - 35 minutes or until golden and crisp.
Cool for 5 minutes and remove from the tin.