Heat olive oil in a large pot over medium heat. Add onion and sauté until softened, about 5 minutes. Add garlic and cook for another minute.

Add the canned tomatoes (with their juice) to the pot. Break them up with a spoon.

Pour in the stock and bring the mixture to a boil. Reduce heat and let simmer for 20 minutes.

Use an immersion blender to puree the soup until smooth, or transfer it to a blender in batches.

Stir in the heavy cream and sugar, if using. Season with salt and pepper to taste.

Ladle into bowls, garnish with fresh basil leaves, and serve warm.