Method
Preheat the oven to 160C/Gas Mark 4.
Heat 1 tbsp oil in a flameproof casserole dish and fry the partridges for about 5 mins, turning several times until well browned on all sides. Transfer to a plate. Meanwhile par-boil the potato slices in a large pan of boiling water for 2 mins only. Drain and rinse in cold running water.
Add the remaining oil to the casserole; fry the leeks for 3-4 mins, stirring occasionally until browned. Stir in the flour, scraping up any juices stuck to the bottom of the pan. Remove from the heat. Gradually stir in the stock and then the cider, thyme and brown sugar.
Return the partridge to the casserole, pushing them amongst the vegetables. Season with salt and freshly ground black pepper. Cover with overlapping slices of potato and dot with the butter. Bake for 1¼-1½ hours or until the potatoes are tender and golden brown.