Vegetable - cooked top until solid (5)
I believe the answer is:
chard
'vegetable' is the definition.
(I know that chard is a type of leaf vegetable)
'cooked top until solid' is the wordplay.
I cannot really see how this works, but
'solid' could be 'hard' (associated in meaning) and 'hard' is found in the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for chard that I've seen before include "Vegetable; Somerset town" , "Kind of (Swiss?) beet with edible leaves" , "Beet with edible leaves and stalks" , "Leaf stalks from a kind of beet" , "Variety of beet with edible white leaf stalks" .)