Add pane, unusually, that is completely blank (7)
I believe the answer is:
deadpan
'completely blank' is the definition.
'deadpan' can be an answer for 'blank' (I've seen this before). I am unsure of the 'completely' bit.
'add pane unusually' is the wordplay.
'unusually' indicates anagramming the letters.
'add'+'pane'='addpane'
'addpane' with letters rearranged gives 'DEADPAN'.
'that is' acts as a link.
Can you help me to learn more?
(Other definitions for deadpan that I've seen before include "Showing no expression" , "Poker-faced" , "Dry" , "without a flicker" , "Betraying no emotion" .)