BrooklynJay ~~ still extant, but probably a bit old-hat slang nowadays. Not sure what it ever had to do with the sort of toasted muffin with holes; perhaps a sort of distant rhyming allusion to 'strumpet'?, tho Partridge gives comparison with 'buttered bun' -- perhaps something to do with sliding in easily? It is used rather as a collective term for sexy women generally, than for 'a sexy woman' as you render it, one at a time ~~ e.g. "Good party ~ plenty of crumpet!". Of an individual woman, one would rather say "She's a nice bit of crumpet", than just "She's a nice crumpet".

HTH

~Michael~