Green’s Dictionary of Slang

Aberdeen cutlet n.

[the Aberdeen fishing trade]

a dried haddock.

[UK]London Dly News 1 Feb. 4/7: An ‘Aberdeen cutlet’ is a dried haddock.
[UK]Farmer & Henley Sl. and Its Analogues.
[UK]Yorks. Eve. Post 12 Feb. 10/6: A dried haddock can be known as an ‘Aberdeen cutlet’.
[UK]W. Granville Sea Sl.
I. Doig Dance at the Rascal Fair 21: ‘Mahogany horse at dinner, Aberdeen cutlet at supper.’ Which was to say, dried beef and smoked haddock.