Heat the oil in a medium saucepan and fry the onion, garlic and cumin seeds for 3–4 minutes. Add the cauliflower, potato, stock and milk and bring to the boil. Reduce the heat and simmer for 15 minutes.
Transfer the soup to a blender or food processor and purée until smooth. Stir through the crème fraîche and coriander and season to taste with salt and pepper. Heat through and serve with slices of crusty wholemeal bread.