Preheat the oven to 160C/320F/gas 2.5.
To make the filling place a little lard in the bottom of the casserole and brown the partridges on all sides.
Scatter the flour over the birds and stir through.
Cover the birds with the chicken stock and season with salt and pepper and place in the oven for an hour or so or until the meat is falling from the bone.
Remove the casserole from the oven and use the slotted spoon to transfer the partridges to a chopping board. Take all the meat off the bone and return to the casserole along with the cayenne pepper. Stir in and leave to cool.
Place the butter and a tablespoon of oil in the frying pan and cook the mushrooms until tender and slightly browned.
Add the parsley and stir in along with salt and freshly ground black pepper. Set aside.
Generously butter the pudding basin.
Place a disc of baking paper at the bottom of the basin.
To make the pastry, mix together the flour, mustard powder, suet and salt and add enough cold water to make a soft dough.
Turn out onto a lightly floured work surface and knead for a few minutes.
Remove one quarter of the dough, wrap in clingfilm and set aside.
Roll out the remaining dough to 4mm thick and make a large round which will line the pudding basin.
Carefully lay the pastry in the basin with 1 cm of pastry overhanging the rim.
Fill the basin with alternate layers of partridge and mushrooms and cover with 100ml of the cooking liquid.
Fold over the overhanging pastry and brush with water.
Roll out the remaining pastry to a round that will exactly fit the top of the pudding basin. Press down to secure it to the base.
Make a pleat in a piece of kitchen foil and cover the basin with it, ensuring that the pleat is placed at the centre of the basin. Secure the foil with string tied under the rim of the basin, making sure you create a ‘handle’ with which you can remove the pudding from the hot water.
Place the pudding in the large-lidded saucepan and fill with boiling water two thirds up the sides of the pudding basin. Bring to the boil and reduce the heat to a simmer.
Cover the saucepan and steam for 3 hours making sure you check the level of the water and top up from the kettle if necessary.
Allow to cool slightly before turning out.
Serve with steamed savoy cabbage flavoured with a few crushed juniper berries.
