Heat the oil in a large pan over a medium heat. Add the onions and cook until soft.
Add the pumpkin and garlic. Reduce the heat and cook, covered, for 10-12 minutes. Stir in the curry powder, half the stock and the sugar. Cook for a further 35-40 minutes.
Add the remaining stock and bring to a simmer. Take off the heat and use a hand blender to blend until smooth. Ladle into mugs and sprinkle over the pumpkin seeds or swirl over the crème fraîche to serve. To add a fun spider-web design, spoon the crème fraîche into a piping bag fitted with a small nozzle. Pipe a spiral on the surface of your soup and pull the tip of a knife from the centre of the spiral to the outer edge a few times to form a web shape.