Brain is quite fatty and not for everyone! Note that in some countries a concern does exist regarding transmission of diseases through beef/lamb brains, and that they may not be available everywhere.
Peel and thinly slice onions. Wash brains carefully in cold water, removing skin and veins. Add warm water, salt, black pepper, vinegar, and onions, and cook over medium heat for 10-15 minutes. Drain water taking care not to crush brains. Allow to cool. Slice to a 1cm thickness.
Wash and finely chop the herbs. Add to eggs with salt and black pepper and mix well. Pour flour on both sides of brain slices, then dip each side in the egg-mix and fry in butter on both sides until golden. Serve with Iranian, middle-eastern or pitta bread.