01 - Preheat the oven to 400°F. Arrange tomatoes cut side up and the sliced garlic head on a baking sheet. Drizzle with 1 tablespoon olive oil and season with salt and black pepper. Roast for 30 minutes until tomatoes soften and garlic turns golden and fragrant. Let cool slightly.
02 - Heat the remaining 1 tablespoon olive oil in a large pot over medium heat. Add chopped onion, diced carrot, and celery. Sauté for 5 to 7 minutes until softened and aromatic.
03 - Extract the roasted garlic cloves from their skins and add them to the pot. Add the roasted tomatoes with their juices, dried thyme, and red pepper flakes if using.
04 - Pour in the vegetable broth and bring the mixture to a gentle simmer. Let cook for 10 to 15 minutes, stirring occasionally to meld flavors.
05 - Remove the pot from heat and blend the mixture to a smooth consistency using an immersion blender or in batches with a countertop blender, allowing to cool slightly before blending if needed.
06 - Return the pureed soup to the pot, stir in the heavy cream, and gently reheat without boiling. Adjust salt and pepper to taste.
07 - Ladle the warm bisque into bowls and garnish with fresh basil leaves and a drizzle of olive oil or additional cream if desired.