Preheat the oven to 200ºC, fan 180ºC, gas 6. Place the chicken in a roasting tin, drizzle over half the olive oil and season. Roast for 1 hour and 30 minutes. Add the squash to the tin for the final half hour of cooking time, turning in the juices. Meanwhile, heat a pan with the rest of the olive oil and cook the leeks for 15 minutes.
Make up the stock using the ½ stock cube and 200ml boiling water. Add the cheese, cornflour and stock to the pan, then stir over the heat for a couple of minutes.Add in the roasted squash and leave to cool.
Carefully take the chicken off the carcass, then discard the skin and bones. Shred with a fork and add to the leeks mixture along with the ham slices.
To assemble the pies, lightly brush some melted Butterlicious on the insides of 2 x 5cm deep, 22cm base diameter tins, and brush over one sheet of the filo pastry. Lay the sheet across the base of the tin, overlapping over the side. Use all the sheets in the pack (half for each pie) to go all the way round each tin like the spokes of a wheel.
Divide the mixture between the two pies and fold the overlapping filo in over the top of each pie.
Brush each one generously with Butterlicious. Bake one pie for 40-45 minutes. To freeze the other pie, cool it completely and freeze for up to 1 month. Defrost and cook as instructed in recipe above or cook from frozen, doubling the cooking time. Check that the pie is piping hot in the middle before serving.