I wonder why this recipe has eluded me until now? It is in my battered and well-thumbed copy of Delia's 'Complete Cookery Course' which is well over 20 years old. Perhaps it is the lack of a photo? Anyway, it is supremely good, using puff pastry rather than mash (I used a sheet of bought puff rather than the home-made flaky in the recipe). I can do no better than point you to the recipe on her website, and use her picture - mine was pretty-much like hers but without the fancy pastry shapes on top - couldn't be arsed.