Tip for cooking tough vegetable (5)
I believe the answer is:
chard
'vegetable' is the definition.
(I know that chard is a type of vegetable)
'tip for cooking tough' is the wordplay.
'tip for' says to take the initial letters (one end or tip of the word).
'tough' becomes 'hard' (associated in meaning).
The initial letter of 'cooking' is 'c'.
'c'+'hard'='CHARD'
(Other definitions for chard that I've seen before include "vegetable crop" , "Vegetable with edible leaves and stalks" , "Variety of beet with edible white leaf stalks" , "A beet; sounds like burnt" , "salad" .)