Preheat your oven to 400°F (200°C).
Place the halved tomatoes, chopped onion, and garlic on a baking sheet.
Drizzle with olive oil and season with salt and pepper.
Roast in the oven for 25-30 minutes until caramelized.
Remove from the oven and allow to cool slightly.
Transfer the roasted vegetables to a blender.
Add vegetable broth and dried basil to the blender.
Blend until smooth and creamy.
Pour the mixture into a pot and heat over medium heat.
Stir in heavy cream if desired, and simmer for 5 minutes.