Melt butter in saucepan. Turn heat to low. Add onion, potato and celery and fry gently for about 5 minutes. Stir to prevent sticking.
Cover with hot water; add salt, pepper, nutmeg and crumbled chicken stock cube. Bring to the boil. Cover and simmer on low till vegetables are cooked. This only takes 10 to 15 minutes. Blend soup in blender a cup at a time. Add milk or cream to taste just before serving.