Heat 1 tbsp olive oil in a large saucepan. Add the onion and celery and fry for 10-15 mins, or until starting to soften, then add the garlic and cook for 1 min more. Stir in all the other ingredients, except for the pesto and remaining oil, and bring to the boil.

Reduce the heat and leave to simmer for 6-8 mins, or until the pasta is tender. Season to taste, then ladle into bowls.

Stir the remaining oil with the pesto, then drizzle over the soup. Serve with chunks of crusty bread.