Pre-heat oven to 220°c. Combine the tomatoes, garlic, onion, balsamic vinegar, oil, salt, pepper and sugar in a bowl. Mix to coat before transferring to an oven proof tray. Bake in the oven for 45 minutes.
Transfer the tomatoes to a large pot. Add broth, tomato paste, lentils and bay leaves. Bring to a boil, then cover and simmer for 30 minutes. Remove bay leaves and turn off the heat.
Using a hand blender, blend the soup. I like it smooth but can be left chunkier depending on your preference. Serve soup hot topped with some fresh basil leaves and crusty bread on the side.