Pre heat the oven to gas Mark 4/180c.
Pop the chopped butternut squash and sweet potatoes onto a baking tray and roast for 1 hr or until they are soft. Leave them to cool for a little.
Add the onion for 10 minutes in a saucepan with the olive oil until soft and browning.
Add the garlic and ginger to the onions (I grated them in as it saves time chopping) and fry for 1 minute, then add the spices. Stir to combine.
Add the vegetable stock, sweet potatoes and squash, briefly bring to the boil then reduce the heat.
Blend with a hand blender or food mixer until smooth. Add more water if the consistency is too thick.
Add in tahini and coconut yogurt and stir through. Season well and stir in the chilli flakes.
Serve with a swirl of coconut yogurt, chopped coriander or thyme and a sprinkle of dukka or pine nuts (optional).