Toss the halved tomatoes, quartered onion and peeled garlic cloves with the olive oil, salt and pepper until evenly coated.
Preheat the air fryer to 400°F (200°C) for 3–5 minutes.
Arrange the vegetables cut side up in a single layer in the air fryer basket. Work in batches if needed so nothing overlaps.
Air fry for 25–30 minutes, until the tomatoes have collapsed and the edges are lightly charred.
Transfer the roasted vegetables and any juices from the basket to a blender. Add the sugar, basil and about half of the broth. Blend until smooth, or pulse for a chunkier texture.
Pour the blended soup into a pot, add the remaining broth and bring to a simmer over medium heat.
Stir in the heavy cream, Parmesan and garlic powder. Taste and adjust salt and pepper.
Simmer 8–10 minutes so the flavors come together.
Serve hot, topped with extra basil, Parmesan or a drizzle of olive oil.