Melt the butter in a large frying pan over a fairly high heat and saute the potatoes and onion, shaking the pan from time to time until the potatoes are a light golden brown.

Add half of the water and cook uncovered for about 10 minutes, or until the water has evaporated. If the potatoes are not sufficiently cooked, add the other half of the water and again allow it to evaporate.

Pour the cream over the potato and onion mixture, season with salt and pepper and bring almost, but not quite, to the boil.

Simmer gently for a further 5 minutes, until the cream has thickened into a smooth sauce.

Spoon into a serving dish and garnish with the parsley.