1. Preheat the oven to 190°C. Grease a large baking sheet.
2. Heat the butter in a saucepan and fry the mushrooms until cooked and golden brown. Season.
3. Add the cooked onion, chicken, flour and stir well.
4. Add the milk, chicken stock and stir it well into the chicken mixture.
5. Allow the mixture to simmer on low heat for a few minutes, stir regularly.
6. Remove from the heat, stir in the cheese and set aside to cool completely.
7. Roll out the puff pastry into a 25 x 35cm rectangle. Divide in three lengthways. Only mark, do not cut.
8. Spoon the filling onto the centre third. Cut the pastry on either side of the filling into 2cm wide strips, right up to the filling.
9. Brush the strips with the egg wash. Fold strips alternately over the filling to obtain a pretty plaited effect.
10. Place the plaited chicken pie on the prepared baking sheet and brush with more egg wash.
11. Bake for about 30 minutes until golden brown.

OPTIONAL
* Sprinkle sesame seeds over the egg-washed pastry, just before you place the pie in the oven.
Enjoy!