Heat olive oil in a large pot over medium heat. Add chopped onion and cook for about 5 minutes until translucent. Stir in minced garlic, dried thyme, dried basil, and optional crushed red pepper flakes.

Pour in the canned tomatoes with juices, breaking them up with a spoon. Add vegetable broth and sugar, stirring to combine.

Bring the soup to a simmer and cook uncovered for 20-25 minutes, stirring occasionally.

Remove from heat and blend the soup until smooth using an immersion blender or by transferring to a regular blender.

Stir in the heavy cream and season with salt and pepper. Gently reheat without boiling.

Ladle into bowls and garnish with fresh basil leaves before serving.