Son’s preparing potatoes? Excellent (8)
I believe the answer is:
smashing
'excellent' is the definition.
(thesaurus)
'son's preparing potatoes?' is the wordplay.
I cannot quite see how this works, but
'son's' could be 's' and 's' is present in the answer.
'potatoes?' could be 'mash' (mashed potato) and 'mash' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for smashing that I've seen before include "Great" , "2 [COOL] or 3 [DANDY] perhaps, possibly 20d [WICKED] or 22 [GEAR] !" , "Breaking things - super!" , "Wonderful" , "Excellent; breaking" .)