Arrange the parsnips and onions in a large roasting tin in a single layer, then drizzle with the oil and honey. Sprinkle with the turmeric, crushed chillies and garlic.
Roast in a preheated oven, 190°C (375°F), Gas Mark 5, for 45–50 minutes, turning once until a deep golden brown with sticky, caramelized edges.
Transfer the roasting tin to the hob, add the stock, vinegar and salt and pepper and bring to the boil, scraping up the juices from the base of the pan. Simmer for 5 minutes.
Allow the soup to cool slightly, then purée in batches in a blender or food processor until smooth. Pour into a saucepan and reheat. Taste and adjust the seasoning and top up with a little extra stock, if needed. Mix the cream, ginger and a little pepper together. Ladle the soup into bowls and drizzle the ginger cream over the top, then garnish with a little turmeric, if liked. Serve with croûtons (see