Preheat your oven to 400°F (200°C). Spread the peeled and seeded butternut squash chunks and sliced carrots on a baking sheet. Drizzle with olive oil and toss to coat evenly.
Roast the vegetables in the oven for about 30-40 minutes, until they are golden and caramelized around the edges and feel tender when pierced with a fork.
While the vegetables roast, sauté the chopped onion and minced garlic in a pot with a little olive oil until fragrant and translucent, about 5 minutes.
Remove the roasted vegetables from the oven and let them cool slightly. Transfer the roasted pieces to a blender or add them to the pot with onion and garlic if using an immersion blender.
Add the roasted vegetables to the blender, pour in the vegetable broth, and blend until smooth and creamy. If using an immersion blender, blend directly in the pot until velvety.
Return the blended soup to the stove if using a blender. Warm over low heat, stirring occasionally, until steaming and heated through about 5 minutes.
Season the soup with salt and pepper to taste, stirring to incorporate the flavors evenly.
Serve the soup hot in bowls, garnished as desired with herbs, a drizzle of olive oil, or a sprinkle of sautéed pumpkin seeds.
