Halve the duck legs by cutting each through the joints. Mix the cinnamon with a little salt and pepper and rub over the duck legs. Arrange in a large roasting tin and roast in a preheated oven, 150°C (300°F), Gas Mark 2, for 1¼ hours.
Drain off most of the fat in the roasting tin, leaving just enough to coat the vegetables. Increase the oven temperature to 200°C (400°F), Gas Mark 6.
Add the potatoes, turnips, garlic and thyme to the roasting tin, turning them in the oil and seasoning lightly with salt and pepper. Return the roasting tin to the oven for 45 minutes until the vegetables are deep golden, turning frequently. Meanwhile, string the redcurrants by passing them between the tines of a fork.
Transfer the duck legs and vegetables to warmed serving plates and keep warm. Drain off the excess fat in the roasting tin, leaving the meaty juices. Add the stock, redcurrant jelly and crème fraîche and bring to the boil on the hob. Cook until slightly reduced and thickened. Stir in the redcurrants, season to taste with salt and pepper and heat for 1 minute. Spoon over the duck to serve.