Preheat the oven to 180C/350F/Gas 4.
Heat the olive oil in a very large, ovenproof frying pan over a medium heat. Season the partridges all over, to taste, with salt and freshly ground black pepper. Lay one slice of streaky bacon over the breast of each partridge.
When the pan is hot, add the partridges, breast-side down, and fry for 1-2 minutes, or until browned. Continue to turn the partridges, cooking until browned on all sides.
Transfer the pan to the oven and roast the partridges for a further 10-12 minutes, or until cooked through. (NB: The partridges are cooked through when the juices run clear when the partridges are pierced in the thickest part using a skewer.) Remove from the oven and set aside to rest on a warm plate for five minutes. Reserve the pan and its juices.
Meanwhile, for the spiced apple sauce, bring the apple wedges and cider to the boil in a large frying pan. Reduce the heat to a simmer and continue to simmer for 12-15 minutes, or until the apple wedges have broken down to the consistency of apple sauce. Strain the softened apple mixture through a fine sieve.
Weigh the strained apples, then weigh out half of the apple weight of sugar (this procedure will give the correct measurement of one part sugar to two parts apple mixture.)
Heat the apple mixture, sugar, cinnamon, cloves and mixed spice in a saucepan until all of the moisture has evaporated, about 20 minutes. (NB: The apple mixture is ready when a spoonful of the mixture placed onto a plate does not release any liquid.)
Meanwhile, for the walnut sauce, bring the beef stock to a simmer over a low heat. Continue to simmer for 6-8 minutes, or until the volume of stock has reduced to 150ml/5fl oz.
Blend the warm, reduced stock and the walnut oil in a food processor until the mixture is thick and glossy. Squeeze in the lemon juice. Set aside.
Blanch the kale in a large pan of boiling, salted water for 2-3 minutes. Drain well and refresh in ice cold water. Drain again and set aside.
Just before serving, heat the butter in the frying pan you used to cook the partridge. Remove the bacon from the partridge breasts and chop into pieces. When the butter is foaming, add the bacon and curly kale, and season, to taste, with salt and freshly ground black pepper. Continue to cook for 1-2 minutes, stirring well, until warmed through.
To serve, mix together the walnuts, marjoram and rapeseed oil in a bowl until well combined. Set aside.
Spoon the spiced apple sauce into a piping bag. Dot the plate with small spots of spiced apple sauce. Spoon the kale and bacon mixture into the centre of each of four serving plates. Carve the legs and breast away from the partridges, placing the meat back onto the carcass for presentation. Place each partridge on top of the kale and bacon mixture. Drizzle over the walnut sauce. Spoon the walnut and marjoram dressing around the edge of each plate.