Gather all ingredients.
Preheat oven to 450 degrees F (230 degrees C). On a large rimmed baking sheet, toss tomatoes with onion, garlic, olive oil, salt, black pepper, and crushed red pepper, if using, until vegetables are evenly coated.
Roast in a preheated oven until juices are released and vegetables are very soft and charred in spots, 35 to 40 minutes.
Transfer roasted vegetable mixture to a blender along with cream, basil, and brown sugar. Secure lid on blender, and remove center piece to allow steam to escape. Place a clean towel over the opening. Process until smooth, about 1 minute. Season with salt to taste.
Pour soup into bowls and garnish with a drizzle of olive oil, cracked black pepper, and thinly sliced basil leaves.