Cake ingredient is hard to display (8)
I believe the answer is:
flourish
'display' is the definition.
(flourish is a kind of display)
'cake ingredient is hard' is the wordplay.
'cake ingredient' becomes 'flour' (I've seen this in another clue).
'hard' becomes 'h' (abbreviation used in pencil classifications).
'flour'+'is'+'h'='FLOURISH'
'to' acts as a link.
(Other definitions for flourish that I've seen before include "Fanfare!" , "Thrive; ornamental passage of music" , "Prosper - display" , "show off" , "Bloom" .)