Writing about additional blanket (7)
I believe the answer is:
smother
'blanket' is the definition.
(I've seen this before)
'writing about additional' is the wordplay.
'writing' becomes 'MS' (abbreviation for manuscript).
'about' is a reversal indicator.
'additional' becomes 'other' (I've seen this in another clue).
'ms' backwards is 'sm'.
'sm'+'other'='SMOTHER'
(Other definitions for smother that I've seen before include "Extinguish (fire) by covering it" , "2 (anag)" , "Suffocate, stifle" , "Prevent from breathing" , "don't give enough freedom" .)