This is a great family dish in France.
Put the lard in a large saucepan and, when hot, put in the duck. Cook slowly, turning the duck occasionally till a nice golden colour. Remove from the saucepan, stir in the flour and, when it is a good golden colour, dilute with the hot stock. Skim off the fat as it rises. Now pour the sauce through a sieve into a basin, rinse the saucepan thoroughly and put the sauce back in it, with the duck. Cover closely and simmer very gently for 25 to 30 minutes. Peel the turnips and trim them, cut in thick round slices, and cook in butter, sprinkling a little sugar over them, till they begin to brown. Then add them to the duck, cover and simmer for another 40 minutes. To serve, put the duck on a hot dish, with the turnips around, and strain the gravy over the whole.