Melt butter in a pan over low heat; add garlic and chopped onion. Fry until soft. Add chopped pumpkin and fry, stirring from time to time, for about 10 minutes.
In a separate pot, heat the stock and add the fried pumpkin mixture. Cook for 5 minutes; season with salt and pepper. Set aside to cool slightly, then mix until smooth with an immersion hand blender.
Add sunflower seeds to a dry fry pan and fry them for 2-3 minutes.
Pour the soup into bowls, add a swirl of cream and garnish with toasted sunflower seeds.