Intensely serious article penned by Hemingway, perhaps (7)
I believe the answer is:
earnest
'intensely serious' is the definition.
(I've seen this before)
'article penned by hemingway perhaps' is the wordplay.
'article' becomes 'a' (indefinite article).
'penned by' is an insertion indicator.
'hemingway perhaps' becomes 'ernest' (Ernest Hemingway).
'a' inserted into 'ernest' is 'EARNEST'.
(Other definitions for earnest that I've seen before include "Determined - heartfelt" , "Oscar Wilde play 'The Importance of Being . . . . . . .'" , "Fixed" , "Sincere; determined" , "money put down" .)