Make small dish to hold one tart without filling (8)
I believe the answer is:
belittle
'make small' is the definition.
(I've seen this before)
'dish to hold one tart without filling' is the wordplay.
'dish' becomes 'belle' (I've seen this before).
'to hold' is an insertion indicator.
'one' becomes 'I' (Roman numeral).
'without filling' means to remove the middle letters.
'tart' with its middle taken out is 'tt'.
'i'+'tt'='itt'
'belle' enclosing 'itt' is 'BELITTLE'.
(Other definitions for belittle that I've seen before include "Speak of as having limited worth" , "Imply that thing or person is of little value" , "Imply that person or thing is unimportant" , "Criticise" , "Humiliate" .)