Stupid talk about a singular cook (5)
I believe the answer is:
roast
'cook' is the definition.
(I know that cook is a is a more specific form of the action of roast)
'stupid talk about a singular' is the wordplay.
'stupid talk' becomes 'rot' (I can't explain this - if you can you should give a lot more credence to this answer).
'about' indicates putting letters inside.
'singular' becomes 's' (abbreviation in grammar).
'a'+'s'='as'
'rot' going around 'as' is 'ROAST'.
Can you help me to learn more?
(Other definitions for roast that I've seen before include "Oven-cooked joint" , "Carpet" , "open-air party in US" , "Trash" , "Traditional Sunday lunch" .)