Pithivier of chicken, squash and sage

Preheat the oven to 190°C/gas mark 5

Remove the tough outer skin of the butternut squash and cut the flesh lengthways into three or four long slices, each around 2cm in thickness. Place each slice on a piece of tin foil. Sprinkle with salt and fold up the foil to make a sealed parcel. Roast the parcels in the oven for 30-40 minutes until the squash is just cooked

While the butternut squash is cooking, pour the chicken stock into a large saucepan, add a pinch of salt and heat until just boiling

Poach the chicken breasts in the simmering stock for 15-20 minutes until cooked through. Remove the pan from heat and leave the chicken to cool in the stock

Heat some salted water in a separate pan. When it starts to boil, add the spinach. After 1 minute, drain off the cooking water and plunge the spinach into iced water to halt the cooking process

Wrap the spinach in kitchen paper and squeeze to remove any excess water. The components of the pithivier filling need to be as dry as possible; if the filling is too wet, the pastry around it will go soggy

Chop the cooked spinach, keeping the pieces relatively large

When the chicken breasts have cooled, carefully lift them out of the stock and pat with kitchen paper until dry. Cut into small cubes with a sharp knife

Next, prepare the Portobello mushrooms by pulling off the stalks and removing the skins. Cut the peeled mushrooms into chunks and cook in a hot frying pan for 5-6 minutes, then tip onto kitchen paper and leave to dry

Open one packet of puff pastry and roll out on a lightly floured surface. Stop rolling when the pastry is roughly ½cm thick. Cut out a circle 20cm in diameter. Repeat with the second packet of puff pastry but this time make the circle slightly larger

Lay the smaller circle of puff pastry on a baking tray and place the cooked butternut squash slices in the centre, leaving a small gap all around the edge. You might need to trim the squash to make it fit

Mix together the spinach, chicken mushroom and sage and heap in a dome-shaped pile on top of the squash

Cover the dome with the larger circle of puff pastry. Press the pastry onto the filling to ensure a snug fit then push down firmly all around the edge to seal the pithivier

Leave the pithivier to rest in the fridge for 1 hour, then use a pastry brush to coat the outside with a thin glaze of egg yolk

Make a steam hole in the centre of the pithivier. With the point of a knife, trace a series of curved lines from the hole to the edge of the dome. Press gently to score the surface of the pastry, making sure that you do not cut all the way through to the filling. Keep adding lines until the entire dome is covered with a swirling star-like pattern

Put the pithivier back in the fridge and chill for another 15 minutes. Meanwhile, preheat the oven to a temperature of 200⁰C/gas mark 6

Transfer the pithivier from the fridge to the oven and bake for 10 minutes. Reduce the temperature to 180⁰C and continue to bake for another 30-40 minutes until the puff pastry is golden and crisp

Remove from the oven and serve with steamed beans or seasonal vegetables