For this pudding turn gas to zero (4)
I believe the answer is:
sago
'for this pudding' is the definition.
(I've seen this before)
'turn gas to zero' is the wordplay.
'turn' says the letters should be written backwards.
'to zero' becomes 'o'.
'gas' in reverse letter order is 'sag'.
'sag'+'o'='SAGO'
(Other definitions for sago that I've seen before include "Type of milk pudding" , "Starchy grain used in desserts" , "Powdery starch used in cooking" , "Starchy pudding cereal" , "Powdery starchy food" .)