Cut the skin off the pumpkin, scrape away any seeds or stringy part and cut the flesh up roughly. Peel the sweet potatoes and cut into smallish cubes. Peel and slice the onions.
Melt the butter in a large, heavy-based saucepan over a medium heat, add the onions and fry until golden brown. Add the pumpkin, sweet potatoes and chicken stock, sprinkle with sea salt and bring to the boil. Co