Heat olive oil in a large pot over medium heat.
Add diced onion and sauté until translucent, about 5 minutes.
Stir in minced garlic and cook for 1-2 minutes until fragrant.
Add chopped tomatoes and cook for another 5 minutes.
Pour in vegetable broth and bring to a boil.
Reduce heat and simmer for 15 minutes.
Add fresh basil leaves and sugar (if using).
Use an immersion blender to puree the soup until smooth.
Stir in heavy cream for added richness, if desired.
Season with salt and pepper to taste before serving.