How do you "butterfly" fillet whiting?

[MulletMan]

I saw in a local fish shop the other day where the headed whiting fillets had been cut down the complete underside and then split open - like a butterfly prawn - and completely deboned! How the hell would you do that without losing most of the flesh I wonder?

[devocean]

Just fillet the same but just leave a little bit behind the head on each side and pull the backbone away. Taste beautiful