Heat a large pot over medium heat. Add butter and onion, cook for 6 minutes until onions are slightly browned. Add squash and cook for another 6 minutes, stirring occasionally. Squash and onions should smell very sweet and fragrant.
Add liquid and salt. Bring to a boil, cover, reduce heat to a simmer and cook for 15 minutes.
Using an immersion blender or a blender, puree soup.
Serve with a drizzle of cream and pumpkin seeds.