For the filling, heat the olive oil and butter in a pan and fry the leeks, spring onions and mushrooms until softened.
Place in a large bowl with the cooked chicken, feta cheese, herbs and enough cream to make the mixture moist.
Season the filling with lots of freshly ground black pepper and a little nutmeg, to taste. Try the filling and add a little salt if needed. Feta cheese is very salty so you might not need it.
Brush the base of a frying pan with olive oil. Lay some large pieces of pastry over the pan so that it drapes over the sides and brush all over with olive oil, then spoon in half the filling.
Rip a piece of pastry and lay on top of the filling to cover. Brush with olive oil and sprinkle with a little water.
Spoon in the rest of the filling; place more pastry on top in the same way as before to make the top layer, brush with olive oil and sprinkle with water.
Fold the pastry, hanging over the edges of the pan, back over the top to form a nice round pie. Brush again with olive oil and sprinkle lightly with water.
Fry for 6-8 minutes on a low heat, checking all the time so it doesn’t go brown too fast.
Remove from the heat, turn over like a Spanish tortilla by placing a plate over the frying pan and quickly turning the pie upside-down on to the plate. Quickly slide it back into the pan and cook the other side for 6-8 minutes, or until golden-brown.
Place on a round wooden board and cut into large wedges. Serve hot or cold with a green salad or vegetables.