Brown the chicken all over in a non-stick frying pan. Set aside, but reserve the juices in the pan.
Preheat the oven to 200C/400F/Gas 6.
Heat the butter, onion and raisins in an ovenproof saucepan big enough to hold the chicken, and cook until softened. Add the plums, juniper berries, cinnamon, ginger and nutmeg, and stir through. Drizzle in a little honey and pour in orange juice to taste.
Pour in the chicken stock and red wine. Simmer gently for a few minutes, then add a few sprigs of rosemary. Season liberally with salt and freshly ground black pepper.
Add the chicken to the pan, place in the preheated oven and cook for about 1½ hours, basting several times. The plums will stew down and create a sauce to go with the chicken. The chicken will be cooked when the juices from the thigh run clear when pierced with a skewer.
Meanwhile, for the creamy leek dish, heat the reserved juices in the chicken pan and add the butter. Fry the onion and chopped leek, then add the thyme. Pour the single cream over the leeks and season well with salt and freshly ground black pepper. Heat through for a couple of minutes. Serve with the spicy plum chicken.