One with a pouch to cook pilau under ruins (9)
I believe the answer is:
marsupial
'one with a pouch' is the definition.
(marsupials carry their young in pouches)
'cook pilau under ruins' is the wordplay.
'cook' indicates anagramming the letters.
'under' is a charade indicator (letters next to each other).
'ruins' becomes 'mars' (to mar is to ruin or spoil).
'pilau' with letters rearranged gives 'upial'.
'upial' put after 'mars' is 'MARSUPIAL'.
'to' acts as a link.
(Other definitions for marsupial that I've seen before include "Sort of animal" , "Joey maybe" , "An animal like the kangaroo, female with a pouch for carrying young" , "Pouched animal" , "Mammal that carries its young in a pouch" .)