Upper-class religious leader turned up — that's tasteful (5)
I believe the answer is:
umami
'tasteful' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'upper-class religious leader turned up' is the wordplay.
'upper-class' becomes 'u' (similar in meaning).
'religious leader' becomes 'imam' (an imam leads Muslims in prayer).
'turned up' is a reversal indicator.
'imam' in reverse letter order is 'mami'.
'u'+'mami'='UMAMI'
'that's' is the link.
Can you help me to learn more?
(Other definitions for umami that I've seen before include "Savoury flavour" , "Japanese word for pleasant savoury taste" , "Fifth flavour" , "Savoury taste sensation produced by glutamates - I, a mum (anag)" , "meaty taste" .)