Preheat your oven and spread the tomatoes and garlic on a baking sheet. Drizzle with olive oil, season with salt and pepper, and roast until the tomatoes blister and garlic softens. This step intensifies their natural sweetness.
In a large pot, sauté chopped onions in olive oil until translucent. Once soft, add roasted tomatoes, garlic, tomato paste, and vegetable stock. Let the flavors meld together over medium heat.
Use an immersion blender or regular blender to puree the soup until smooth. Return to the pot, stir in cream, and simmer gently to thicken slightly. Taste and adjust seasoning as needed.