Sift the flour into a large mixing bowl with a pinch of salt. Make a well in the centre and add the egg and soured cream, then mix gradually using a wooden spoon, adding the milk if the mixture seems a little thick. Mix in the sweetcorn and half the spring onions.
Heat a little oil in a large non-stick frying pan and fry a heaped tbsp of the mixture in batches for 2-3 minutes, turning halfway, until golden brown.
Combine the remaining ingredients with the remaining spring onions as a salsa, season and serve with the fritters.