Preheat the oven to 400°F (200°C). Prepare a baking sheet lined with parchment paper.

Cut the acorn squash in half lengthwise, scoop out the seeds, brush with olive oil, and sprinkle with salt and pepper. Place cut side down on the baking sheet.

Roast squash for 40 to 50 minutes until edges are brown and flesh is tender.

In a Dutch oven, heat remaining olive oil over medium heat, add onion, carrots, celery, and garlic, and sauté for 5-7 minutes.

Scoop the roasted squash flesh into the Dutch oven, add vegetable stock and herbs. Simmer for 10 minutes.

Blend the soup until smooth using an immersion blender or in batches with a regular blender.

Stir in half and half, adjust seasoning, heat gently, and serve with optional toppings.