Roll is getting dry on the outside: I’d recommend dunking (7)
I believe the answer is:
baptist
'i'd recommend dunking' is the definition.
(person who advocates baptisms - dunking in water)
'roll is getting dry on the outside' is the wordplay.
'roll' becomes 'bap' (I've seen this before).
'getting dry' becomes 'tt' (I am not sure about this - if you are sure you should believe this answer much more).
'on the outside' means one lot of letters goes inside another.
'is' going inside 'tt' is 'tist'.
'bap'+'tist'='BAPTIST'
Can you help me to learn more?
(Other definitions for baptist that I've seen before include "Protestant church member" , "John, for example" , "Variety of Protestant" , "Type of Christian" , "Protestant advocating total immersion at a christening" .)