People in hamlet prepared Swiss cheese (9)
I believe the answer is:
emmenthal
'swiss cheese' is the definition.
(Emmenthal is an example)
'people in hamlet prepared' is the wordplay.
'people' becomes 'men' (man is a kind of person).
'in' indicates putting letters inside.
'prepared' is an anagram indicator.
'hamlet' with letters rearranged gives 'emthal'.
'men' going within 'emthal' is 'EMMENTHAL'.
(Other definitions for emmenthal that I've seen before include "Type of cheese" , "Something cheesy" , "Swiss cheese with holes" , "Hard Swiss cheese" , "Swiss valley giving its name to a cheese" .)