Cheese that's made up (4)
I believe the answer is:
edam
'cheese' is the definition.
(I know that Edam is a type of cheese)
'made up' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'made' reversed gives 'EDAM'.
'that's' is the link.
(Other definitions for edam that I've seen before include "Cheese made badly" , "town in Holland" , "Yellow cheese with a red covering" , "Red-coated cheese" , "something from the deli" .)