Green’s Dictionary of Slang

1. that which settles a situation, a clincher, a finisher.

1869

Daily News 12 May n.p.: Jeames [writes] ‘I expect this will be a cooker for me.’.

2. anything exciting, e.g. a sexy or sophisticated person, an emotive piece of music.

1943		‘Whitman College Sl.’ in AS XVIII:2 Apr. 154/2: some cooker. An attractive girl.
1960, 1975		(ref. to 1940) Wentworth & Flexner DAS 120/2: cooker A sexually attractive girl.
1994		C. Major Juba to Jive 110: Cooker n. (1950s) a hip or swinging person.