1. For the pastry, put the butter and lard in a medium saucepan with 200ml cold water and bring to the boil – as soon as it comes to a boil and the butter and lard have melted, remove from the heat.
2. Put the flour and salt in a large heatproof bowl and make a well in the centre. Crack in the egg, then mix together.
3. Pour the hot water mixture onto the flour, mixing with a spoon to bring the dough together. When it’s cool enough to handle, use your hands to knead the dough until smooth. Leave to cool, covered with a tea towel, until just warm or at room temperature.
4. Wrap a third of the pastry in cling film and put to one side. Roll out the rest of the pastry into a circle approx 30cm in diameter (or larger than your cake tin). Lift into a deep, 23cm diameter, loose- bottomed cake tin.
5. Press the pastry up the sides and over the rim of the tin, making sure it’s even – it should overhang a little and have sharp corners at the bottom. Chill in the fridge, uncovered, for 30 minutes.
6. In a large pan, heat a glug of oil over a medium heat. Gently fry the onions and leeks for 10 minutes, stirring occasionally. Add the mushrooms and garlic, then cook for a further 5 minutes and lightly season. Transfer the vegetables to a bowl and set aside.
7. Add another glug of oil to the pan and turn up the heat. Add the sausages and fry for 5-10 minutes, shaking often, until they start to colour. Return the veg to the pan along with the flour and stir to combine. Fry for 1-2 minutes.
8. Add the cider, bubble to reduce for 2 minutes, then add the stock, ham hock and cream. Simmer for 10 minutes or until the sauce thickens. Season, then stir in the lemon juice and chopped herbs. Leave to one side to cool before adding to your pie pastry.
9. Heat the oven to 200°C or gas mark 6.
10. Remove the pastry from the fridge and pour the cooled filling into the chilled pie case. Tear off a fifth of the reserved pastry and shape into a ring big enough to fit around the top edge of the cake tin (you can do it in 2 pieces if it’s easier).
11. Brush the lip of the pie case with a little of the beaten egg, then press the pastry ring on top. This will create a secure seal for the lid. Roll out the remaining pastry to a circle about 24-25cm in diameter.
12. Brush the lip of the pie case with more beaten egg, then place the pastry circle on top. Crimp the edges together using your forefinger and thumb to seal the pie, then cut off any excess pastry.
13. Brush the top of the pie with more of the beaten egg and pierce a hole in the middle with a knife to let out steam as it cooks. Use the trimmings to decorate the pie, if you like – don’t forget to glaze them as well and leave the hole uncovered!
14. Bake the pie for 20 minutes. Turn down the oven to 180°C or gas mark 4, then continue to bake for a further 40 minutes. Cover with foil if the pie starts to brown too much. Wait at least 30 minutes before slicing into the pie – that way it will hold its shape better. You can also serve it at room temperature, or refrigerate once cooled and serve up in slices cold to enjoy the next day.