Going around Iranian capital and church is a treat! (6)
I believe the answer is:
eclair
'a treat' is the definition.
(type of cake)
'going around iranian capital and church' is the wordplay.
'going around' says the letters should be written in reverse.
'iranian capital' becomes 'rial' (currency of Iran).
'and' says to put letters next to each other.
'church' becomes 'CE' (abbreviation for Church of England).
'rial'+'ce'='rialce'
'rialce' in reverse letter order is 'ECLAIR'.
'is' acts as a link.
(Other definitions for eclair that I've seen before include "Long chocolate cake for Claire" , "Torpedo-shaped cream cake" , "Lacier type of confection" , "Dainty" , "Soft cream cake" .)