Heat the oil in a saucepan over a medium heat and fry the onion and garlic for 8-10 minutes until softened.
Add the tinned tomatoes, tomato puree, vegetable stock and a good pinch of salt and pepper. Pop the lid on the pan and simmer for 15 minutes.
Blitz the soup in a blender, or with a stick blender, until smooth.
Stir in the pesto and balsamic vinegar and serve.
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