Starchy food dad is about to turn to (6)
I believe the answer is:
potato
'starchy food' is the definition.
(I've seen this in another clue)
'dad is about to turn to' is the wordplay.
'dad' becomes 'pa' (synonyms).
'is about' is an insertion indicator.
'turn' says the letters should be written backwards.
'to' in reverse letter order is 'ot'.
'pa' placed around 'ot' is 'pota'.
'pota'+'to'='POTATO'
(Other definitions for potato that I've seen before include "Would be difficult to deal with if hot" , "Tuberous vegetable" , "Root vegetable" , "Plant tuber eaten as a vegetable" , "French wine region" .)