To cook it, do you need a gas ring? (4)
I believe the answer is:
sago
'to cook it do you need a' is the definition.
I can't judge whether this definition defines the answer.
'gas ring?' is the wordplay.
I cannot really understand how this works, but
an anagram of 'gas' is 'sag' which is present in the answer.
'ring?' could be 'o' (letter resembling a ring) and 'o' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sago that I've seen before include "Starchy grain used in desserts" , "Edible palm starch" , "Starchy foodstuff" , "Powdery starch from a palm" , "Powdery starch used in cooking" .)