Dice the onion, carrots, and celery. Mince the garlic. Core and roughly chop the tomatoes.
Heat the olive oil in a large pot over medium heat. Add the onion, carrots, and celery. Cook for 5-7 minutes, stirring occasionally, until softened.
Add the garlic and cook for 1 minute until fragrant.
Add the chopped tomatoes, chicken broth, salt, and pepper. Bring to a boil.
Reduce heat to low, cover, and simmer for 20-25 minutes until the vegetables are very tender.
Using an immersion blender (or working in batches with a regular blender), puree the soup until smooth.
Stir in the butter until melted. Taste and adjust seasoning.
Serve hot, optionally topped with a drizzle of olive oil or a dollop of cream.
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