Dark treacle in short while found by girls (8)
I believe the answer is:
molasses
'dark treacle' is the definition.
(I've seen this before)
'short while found by girls' is the wordplay.
'short while' becomes 'mo'.
'found by' means one lot of letters go next to another.
'girls' becomes 'lasses' (lass can informally mean a girl).
'mo'+'lasses'='MOLASSES'
'in' is the link.
(Other definitions for molasses that I've seen before include "Syrupy stuff" , "Thick dark syrup made from sugar cane" , "Black treacle" , "Dark syrup extracted from sugar cane" , "Dark syrup from raw sugar" .)