Method

1. Preheat the oven to 190°C/gas mark 5
2. Peel the neck end of squash and slice lengthways into long slices about 2cm thick (you will get roughly three slices). Season with salt and a little olive oil and wrap in foil. Bake for 30 – 40 minutes until just cooked. Turn the oven up to 200°C/gas mark 6
3. Meanwhile, add the chicken stock to a large pan and bring to a gentle simmer. Add the chicken breasts and poach for 15 – 20 minutes. Once the chicken is cooked through, allow to cool in the poaching liquid
4. Fill another large pan with salted water and bring to the boil. Blanch the spinach for 1 minute, then quickly drain and refresh in iced water. Squeeze out any excess moisture from the spinach using kitchen towel and roughly chop
5. Remove the chicken from the stock and pat dry on kitchen paper, chop into small pieces
6. Pan fry the mushrooms for 5 – 6 minutes and drain on kitchen paper (it is important that all the filling components are dry, otherwise the pastry will become soggy)
7. Mix together the chicken, spinach, sage and mushrooms and reserve
8. To assemble the pithivier, lightly dust a clean work surface with flour and roll one packet of the pastry out so that it is about ½ cm thick. Trim the edges to create a circle (roughly 20cm in diameter) and place on a baking tray
9. Roll the other packet to the same thickness and trim to form a slightly larger circle, keep to one side
10. Arrange the slices of squash over the base of the pastry, leaving a thin border around the edge (you may need to trim the squash slices to make them fit)
11. Pile the chicken mixture on top of the squash to make a domed shape
12. Place the larger piece of pastry over the top, and press so that it fits tightly around. Push down on the border with your fingers to seal. Transfer to the fridge for 1 hour to firm up
13. When the pastry has chilled, remove from the fridge and brush with the egg yolks to glaze. To score the pastry, very gently run a knife in semi-circles down from the centre of the pastry to the edges. Return to the fridge to rest for a further 15 minutes
14. Bake the pithivier for 10 minutes, then turn the oven down to 180°C and bake for a further 30 – 40 minutes until the pastry is golden brown
15. Serve with some simple steamed beans, or seasonal vegetables