In a large saucepan, sauté onion and garlic in butter until soft. Add carrots, celery, pepper, tomato paste, lime juice, sugar, salt, paprika, and cayenne. Cook for another 5 minutes.
Add broth and tomatoes, and simmer mixture for 20 minutes, until veggies are softened.
In a blender or food processor (in 2 batches), pureé until smooth, then return to pot to simmer until ready to eat.