Peel, deseed and dice the butternut squash.
Peel and finely chop the onions.
Heat the oil in a large saucepan. Add the onions and cook gently until soft. Add the squash and garlic. Reduce the heat and cook, under cover, for 10 minutes.
Add the curry powder, stir, then pour in half of the stock. Add the sugar. Cook for a further 35 minutes.
Add the remaining stock and bring to the boil. Turn off the heat and, using a hand-held blender, process until smooth and creamy.
Serve in a bowl or mugs, with the pumpkin seeds sprinkled on top and with a spoonful of yoghurt if you like.