Preheat your oven to 400°F (200°C). Toss the butternut squash chunks with olive oil, then spread them evenly on a baking sheet.
Roast the squash in the oven for about 30-40 minutes, until the pieces are golden and caramelized around the edges, and very tender when pierced with a fork.
Meanwhile, sauté the chopped onion in a large pot over medium heat until translucent and fragrant, about 5 minutes.
Add the minced garlic to the onions and cook for another minute, until the garlic is just fragrant.
Remove the roasted squash from the oven and let it cool slightly, then add the soft squash to the pot with the onions and garlic.
Pour in the vegetable broth, then bring the mixture to a gentle simmer. Let it cook for 10 minutes to allow flavors to meld.
Use an immersion blender or transfer the soup in batches to a blender, and blend until smooth and velvety in texture.
Stir in the heavy cream for added richness, and season with salt and pepper to taste.
Return the soup to a gentle simmer for another few minutes, allowing the flavors to meld and the soup to heat through.
Taste and adjust the seasoning as needed, then ladle into bowls and serve hot, garnished if desired.
