Learner introduced to writer mounting current Russian course (5)
I believe the answer is:
blini
'russian course' is the definition.
(type of Russian dish)
'learner introduced to writer mounting current' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'introduced to' is an insertion indicator.
'writer' becomes 'nib' (something which writes).
'mounting' says the letters should be written backwards (going up in a down clue).
'current' becomes 'I' (symbol for electric current).
'l' put inside 'nib' is 'nilb'.
'nilb' backwards is 'blin'.
'blin'+'i'='BLINI'
(Other definitions for blini that I've seen before include "Pancakes served with sour cream" , "Buckwheat pancakes" , "East European pancakes" , "Eastern European twenty four Ac" , "Small buckwheat pancake" .)