Heat olive oil in a large pot over medium heat.
Add chopped onion and sauté until translucent, about 5 minutes.
Stir in minced garlic and cook for another minute.
Add chopped tomatoes and sugar; cook for 10 minutes until tomatoes soften.
Pour in vegetable broth and bring to a simmer.
Reduce heat and let soup simmer for 15 minutes.
Use an immersion blender to puree the soup until smooth.
Season with salt, pepper, and balsamic vinegar if desired.
Serve hot, garnished with fresh basil leaves.
Enjoy with crusty bread on the side!