Preheat your oven to 400°F (200°C).
Place the halved tomatoes, chopped onion, and garlic cloves on a baking sheet.
Drizzle with olive oil, sprinkle with salt, pepper, and sugar.
Toss to coat evenly and spread them out in a single layer.
Roast in the oven for 30-35 minutes until tomatoes are caramelized.
Remove from oven and let cool slightly.
Transfer the roasted vegetables to a pot.
Add the vegetable broth and bring to a simmer.
Use an immersion blender to puree until smooth.
Stir in the fresh basil and adjust seasoning to taste.