Put the water, butter, turmeric, pepper and salt to taste in a large saucepan. Bring to a boil, then tip in the couscous in a steady stream with half the aniseed.
Leave to simmer for 15 minutes over a low heat, stirring from time to time during cooking to prevent lumps from forming. If the couscous swells too much, add a little extra water.
Stir in the remaining aniseed and serve hot.