Melt the butter in a saucepan and fry the onion until softened but not coloured. Add the parsnip, pour in the stock and cook for 6-8 minutes, or until the parsnip is tender.
Add the goats' cheese and curry powder and cook for 3-4 minutes. Stir in the double cream and season with salt and freshly ground black pepper, then blend with a hand-held blender until smooth. Add a dash of boiling water if the soup is too thick.
Pour into a bowl and garnish with a dollop of Greek-style yoghurt and a drizzle of olive oil.