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Add the lemongrass and ginger and cook for 5 minutes. Then add the stock and broad beans. Bring to the boil then simmer for 10-15 minutes.
Pour the soup into a blender or food processor and whizz until you have a puree. Sieve if you wish.
Add the soymilk, season to taste and add the sugar. Serve well chilled, sprinkled with finely chopped mint.
posted by Mr Falafel