Peel and quarter potatoes  finely chop the onions. Melt butter in a saucepan and add the potatoes and onions, cover and simmer for 10 mins. Add vegetable Stock, Salt & Pepper and Nutmeg and stirring continuously until boiling. Reduce heat, cover and simmer for 30 mins, until vegetables are soft, stir occasionally. Remove from heat, cool slightly then run mixture though sieve, then return to the pan. Stir in the milk and cornstarch and bring to the boil, stir continuously. Remove from the heat, sprinkle with chives and parsley.