First of all, prepare the trunips by peeling them carefully and thinly with a potato peeler, then put them into a large saucepan of boiling water and boil for 3 mnutes.
Next, drain in a colander and then return them to the saucepan. Now add just enough stock to cover the turnips, bring this to the boil and simmer (uncovered) for about 3 minutes, or until the turnips are tender. Use a draining spoon to remove the turnips, place them in a warmed serving dish and keep hot while you make the glaze.
Next, blend the mustard with a little of the white wine (or cider) and add to the stock in the saucepan with the remainder of the wine and the sugar. Re-heat, taste and season with salt and freshly milled black pepper. Simmer rapidly (without a lid) until the liquid has reduced to a syrupy consistency, then pour this over the turnips, sprinkle with chopped parsely and serve.