Heat a small frying pan and dry roast the coriander, cumin and cardamon seeds for 2-3 minutes. Crush them finely with a pestle and mortar.
Heat the butter and oil in a saucepan until the butter starts to foam, add the onion and soften gently for 5 minutes. Add the garlic and cook for 2 minutes then add the crushed spices with the turmeric and ginger. Stir and cook for a few minutes,
Add the parsnips, stirring all together, then pour in the stock. Add the seasoning then simmer very gently, uncovered, for an hour.
Remove from the heat and liquidise, then return to the saucepan and check the seasoning.
Peel the apple and as the soup just reaches simmering point grate the apple into it. Simmer for 3-4 minutes.