Heat a large frying pan over a low to medium heat. When the pan is hot, add the butter and onion and fry gently for 8-10 minutes, or until softened but not coloured.
Increase the heat to medium, add the diced pumpkin and continue to fry, stirring well, for 2-3 minutes.
Pour the hot vegetable stock over the pumpkin mixture and bring to the boil. Stir in the parmesan, then return the mixture to a simmer and continue to simmer for a further 8-10 minutes. Season, to taste, with salt and freshly ground black pepper.
Transfer batches of the mixture to a food processor and blend to a smooth purée. Repeat the process until all of the mixture has been blended to a purée.
Strain the soup mixture through a fine sieve into a clean saucepan and heat until warmed through.
Meanwhile, for the garnish, heat a frying pan over a high heat until hot. Add the pumpkin seeds and dry fry until toasted.
Add the vegetable oil and continue to fry the seeds for 4-5 minutes, shaking the pan regularly, until golden-brown.
Heat one teaspoon of the olive oil in a separate frying pan over a medium heat. Add the diced pumpkin and fry for 1-2 minutes, or until just softened. Remove from the pan and set aside.
Return the frying pan used to cook the pumpkin to the heat and add the remaining two teaspoons of olive oil. When the oil is hot, add the ceps and fry for 2-3 minutes, or until golden-brown. Season, to taste, with salt and freshly ground black pepper. Stir in the chives until well combined.
To serve, ladle the warm soup into four bowls. Sprinkle over a pinch of each of the cooked pumpkin, diced parmesan and ceps. Finish with the toasted pumpkin seeds, then drizzle over a little olive oil.