Heat the olive oil in a large pot over medium heat.

Add the diced onion and sauté for 5-7 minutes, stirring occasionally, until softened and translucent.

Add the minced garlic and cook for 1 minute, stirring constantly, until fragrant.

Pour in the canned tomatoes (including their juices) and break them up with a spoon or potato masher.

Add the vegetable broth, sugar, dried thyme, and crushed red pepper flakes (if using). Stir to combine.

Bring the mixture to a simmer, then reduce the heat to low and let it cook uncovered for 20 minutes, stirring occasionally.

Remove the pot from heat and use an immersion blender to purée the soup until smooth. Alternatively, transfer the soup in batches to a blender and blend until smooth, then return it to the pot.

Season the soup with salt and pepper to taste. If desired, stir in the heavy cream for a richer flavor.

Reheat the soup gently over low heat if needed. Serve warm, garnished with fresh basil leaves and accompanied by crusty bread or croutons if desired.