Gas on for potato cake (6)
I believe the answer is:
waffle
This could be a double definition.
'gas on' is the first definition.
(I've seen this before)
'potato cake' is the second definition.
'waffle' can be an answer for 'cake' (waffle is a kind of cake). I'm not certain of the 'potato' bit.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for waffle that I've seen before include "Vague wordy talk or writing" , "Battered cake" , "Talk vaguely and at length" , "Breakfast item - go on and on" , "blather" .)