Potato that is providing iron (6)
I believe the answer is:
mashie
'iron' is the definition.
(mashie is old-fashioned slang for a golf club)
'potato that is' is the wordplay.
'potato' becomes 'mash' (mashed potato).
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'mash'+'ie'='MASHIE'
'providing' acts as a link.
(Other definitions for mashie that I've seen before include "He aims (anag) - golfer's five iron, formerly" , "Old-fashioned golf club" , "Golf club for lofting" , "Old golf club" , "One of 9 [CLUBS]" .)