Rodent grabs seconds for pudding (6)
I believe the answer is:
mousse
'pudding' is the definition.
(I have seen 'Fluffy pudding' mean 'mousse' so perhaps 'pudding' could also mean 'mousse')
'rodent grabs seconds' is the wordplay.
'rodent' becomes 'mouse' (mouse is a kind of rodent).
'grabs' is an insertion indicator.
'seconds' becomes 's'.
'mouse' placed around 's' is 'MOUSSE'.
'for' is the link.
(Other definitions for mousse that I've seen before include "F" , "cold dish" , "Pope's representative" , "Creamy dish" , "Foamy dish" .)