Dutch town built up (4)
I believe the answer is:
edam
'dutch town' is the definition.
(I've seen this before)
'built up' is the wordplay.
'built' becomes 'made' ('make' can be a synonym of 'build').
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'made' in reverse letter order is 'EDAM'.
(Other definitions for edam that I've seen before include "Cheese made badly" , "Made into popular cheese" , "Cheese made in Holland" , "Dutch market town famous for its cheese" , "Dutch food" .)