Peel and dice the squash (seeds removed). Cut the cauliflower into florets. Finely chop the onion.
Heat the oil in a saucepan and gently sauté the onion.
Add the butternut squash and cook for 8 minutes, under cover. Add in the cauliflower and the spices, then stir to coat the veggies well.
Pour in the vegetable broth, then cover with a lid and bring to the boil. Turn down the heat and gently simmer for 20-25 minutes, until the vegetables are tender.
Turn off the heat and, using a stick blender, whizz the mixture until you get a smooth, creamy soup. Add the coconut milk and mix. Season to taste and warm up to simmering point.
Serve with coriander leaves scattered on top (and some dried chilli flakes for extra heat).