Preheat your oven to 400°F (200°C). Toss the cubed butternut squash with olive oil, cinnamon, and nutmeg until evenly coated. Spread the squash on a baking sheet in a single layer.
Roast the squash in the oven for about 25-30 minutes, until the pieces are golden brown and tender when pierced with a fork.
Meanwhile, heat a large pot over medium heat. Add a splash of oil and sauté the sliced onion until soft and translucent, about 5 minutes.
Add the minced garlic to the onions and cook for another minute until fragrant.
Once the roasted squash is ready, transfer it to the pot along with the sautéed onions and garlic.
Pour in the vegetable broth, bringing the mixture to a gentle simmer. Let it cook for about 10 minutes to allow flavors to meld.
Use an immersion blender or carefully transfer the soup in batches to a blender. Puree until silky smooth, then return to the pot.
Season the soup with salt and pepper to taste, adjusting the seasoning as needed.
Warm the soup over low heat if necessary, then ladle into bowls and serve hot, garnished with a drizzle of cream or a sprinkle of herbs if desired.
