It would be much more interesting (producers, are you listening?) to take the celebs to a fancy restaurant (which they know all about in advance) and for them each to have come up with a recipe that fits in with the style of restaurant and teach it to the staff who then have to make it for a lunchtime service, seeing how well it goes down with the customers.
I know it would be a bit harder to get restaurants to sign up to a round that isn't basically free advertising for their food (although it still would allow them to show off a bit) but it would be a lot more entertaining for us to watch Su Pollard gifting a top sous-chef with her ideas and wisdom and seeing what the public thinks.