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I think you could be right about the cheese sauce, I have a feeling it will overwhelm the fish, interesting that you always make a cheese sauce though clover. However, it's made now, all cooked, and very tasty from the small spoonful I've tried.
Next time I'll try just cream and fish stock.
I've lost my cooking mojo at the moment so am trying to make things as easy as possible for myself, hence the frozen mash, which, incidentally, is very, very nice.