Thanks for mashing the rest of the spuds (6)
I believe the answer is:
taters
'the spuds' is the definition.
('tater' can be a synonym of 'spud')
'thanks for mashing the rest' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'for' says to put letters next to each other.
'mashing' indicates an anagram.
'rest' is an anagram of 'ters'.
'ta'+'ters'='TATERS'
'of' acts as a link.
(Other definitions for taters that I've seen before include "Potatoes (dialect)" , "starchy tubers" .)