Preheat the oven to 400°F (200°C). Spread the cubed squash and sliced carrots evenly on a baking sheet. Drizzle with olive oil and toss to coat.
Roast the vegetables in the oven for about 30-40 minutes, until they're tender and caramelized around the edges, filling the house with a warm, sweet aroma.
While the vegetables roast, sauté the chopped onion and minced garlic in a large pot over medium heat until softened and fragrant, about 5 minutes.
Once the roasted vegetables are ready, add them to the pot with the sautéed onions and garlic. Pour in the vegetable broth.
Use an immersion blender to purée the soup until smooth and creamy. Alternatively, transfer the mixture to a regular blender in batches and blend until smooth.
Return the blended soup to the stove, season with salt and pepper to taste, and warm through for another 5 minutes.
Serve the soup hot, garnished with a drizzle of olive oil or a sprinkle of fresh herbs if desired. Enjoy the velvety, caramelized flavor in every spoonful.