In a saucepan melt butter, sauté onion. Add the parsnips and potatoe, sauté for approx 5 minutes. Add curry and stock. Season. Bring the mixture to a boil and reduce the heat. Cover and simmer until vegetables are tender. Puree the vegetables in a blender. Bring back to boil and add cream stirring until the mixture boils. Taste, season and enjoy.