1. Put the stock in a large saucepan and bring to the boil. Add the shallot or onion, garlic, peas and chopped mint. Cook at a brisk simmer for 10 minutes until the peas are tender.
2. Transfer in batches to a blender and blend until smooth. Season to taste and serve immediately in bowls, topped with a swirl of fat-free natural yogurt, if wished.