Strain the stock through a fine sieve, carefully skimming off every particle of fat.
Wash the vegetables, and boil them whole in a stock-pot, or in a pan of salted water. When they are soft, take them out of the pan, cut the cabbage into thin shreds, the leek into strips about an inch long, and the carrot and turnip into neat dice.
Melt the butter in a stewpan; when it is hot put in the vegetables and toss them about lightly in the butter over the fire for five minutes. Have the strained stock ready in a saucepan, drain the vegetables well out of the butter, and add them to the stock. Let it simmer for fifteen minutes, then skim it carefully and season it.