Wash the turnips and place in a pan with the butter and sugar, plus just enough water to cover. (If you are using larger turnips, peel and cut the turnips into wedges first.) Bring to the boil and simmer for 20 minutes, stirring from time to time. Add a little more water if necessary. Add the parsley, seasoning and wine. Simmer until almost all the liquid has evaporated, then serve.