Preheat oven to 400°F (200°C), slice butternut squash in half and scoop out seeds. Place cut side down on parchment-lined baking sheet and roast for 40 minutes until tender.

In a large pot, heat olive oil over medium heat. Sauté chopped onion for 5-7 minutes until translucent, then add minced garlic and cook for an additional 1-2 minutes.

Scoop roasted squash flesh into pot with sautéed onions and garlic. Add vegetable broth and bring to simmer for 10 minutes.

Blend the soup until smooth and creamy using an immersion blender or regular blender in batches.

Return to pot, stir in cream or plant-based milk, season with nutmeg, cinnamon, salt, and pepper. Heat gently for 5 minutes.

Ladle into bowls, garnish with fresh herbs and optional spices. Serve immediately.