Heat the oil in a large deep heavy bottomed saucepan over a medium heat. Add the butter, stir and melt gently.
Sweat the onions down and then add the garlic and ginger. Cook for 1 minute. Stir in the butternut squash and coat well with the onions, garlic and ginger.
Season with salt and ground black pepper. Add the thyme, ground cumin, ground coriander and sweet paprika. Cook out for 1 minute.
Pour over the chicken stock, cover the saucepan with a lid and simmer until the butternut squash starts to breakdown.
Add the coconut milk and continue to simmer for five minutes. The squash by now should be fully broken down and the soup will have a slightly rustic texture. (If you prefer a smoother soup now is the time to pulse with a hand held processor.)
Add the crab meat and prawns a few minutes before serving. Garnish with finely chopped coriander.