Heat a large saucepan or casserole dish, pour in the olive oil, then add the onion, celery, chilli and coriander seeds.
Season to taste then cook, stirring occasionally, for about 10 minutes until the onion has turned silky soft and translucent. Add the garlic and potato and cook for a further few minutes, stirring to coat the potato in oil before finally adding the cauliflower and enough stock or water to cover.
Simmer the broth until the cauliflower is completely tender. Whizz up with a stick blender and taste to check the seasoning, adding more salt and pepper if you think it needs it.