A yarn about accountant that's hot and steamy (9)
I believe the answer is:
americano
'that's hot and steamy' is the definition.
(type of hot drink)
'a yarn about accountant' is the wordplay.
'yarn' becomes 'merino' (type of wool).
'about' means one lot of letters goes inside another.
'accountant' becomes 'ca' (abbreviation for chartered accountant).
'merino' enclosing 'ca' is 'mericano'.
'a'+'mericano'='AMERICANO'
(Other definitions for americano that I've seen before include "Espresso diluted with hot water" , "drink" , "Style of coffee" .)