Steep but popular French practice (6)
I believe the answer is:
infuse
'steep' is the definition.
('infuse' can be a synonym of 'steep')
'popular french practice' is the wordplay.
'popular' becomes 'in'.
'french' becomes 'f'.
'practice' becomes 'use' (use is a kind of practice).
'in'+'f'+'use'='INFUSE'
'but' acts as a link.
(Other definitions for infuse that I've seen before include "Let sit in a liquid to extract a flavour" , "Instil or steep in liquid, as to make tea" , "Breathe into" , "Imbue or instil" , "Soak (tea etc) in liquid to extract flavour" .)