Cut the butternut squash in half, take out seeds and fibres in the middle, then peel. Cut into small chunks. Dice the onion and fry in butter together with the squash in a tall pot. Once the onion is soft, fill up with vegetable stock so that everything is covered. Let boil on a low heat until everything is tender. In the meantime slightly roast the pumpkin seeds.
Add cream, a pinch of cayenne pepper and black pepper. Blend and serve sprinkled with pumpkin seeds and croutons.