Preheat your oven to 400°F (200°C). Cut the butternut squash in half lengthwise and scoop out the seeds.

Place squash halves cut-side down on a baking sheet and roast for about 45 minutes until tender.

In a large pot, heat olive oil over medium heat. Add diced onions and sauté until translucent, about 5 minutes.

Scoop roasted squash flesh into the pot with onions. Add cinnamon stick, curry powder, and cayenne pepper.

Pour in vegetable broth and bring to a gentle simmer for about 10 minutes.

Using an immersion blender, purée the soup until smooth. If needed, use a regular blender but allow it to cool slightly.

Taste and adjust seasoning. Serve warm, garnished with coconut milk or sour cream.