Preheat oven to 400°F (200°C). Toss the cubed butternut squash with 1 tbsp olive oil, a pinch of salt, and pepper on a baking sheet; roast for 20-25 minutes until tender.

While squash roasts, heat the remaining 1 tbsp olive oil in a large pot or Dutch oven over medium heat. Add chopped onion and sauté until softened, about 5-7 minutes. Stir in minced garlic and cook for another minute until fragrant.

Add the roasted butternut squash, vegetable broth, and ground nutmeg to the pot. Bring the mixture to a simmer, then reduce heat and let it cook for 10-15 minutes, allowing flavors to meld.

Carefully use an immersion blender to purée the soup directly in the pot until smooth and creamy. Alternatively, transfer the soup in batches to a regular blender and blend until smooth, then return to the pot.

Taste the soup and adjust seasoning with additional salt and pepper as needed. Serve hot, optionally garnished with fresh parsley or toasted pumpkin seeds.