Italian eatery serves up tart to Victorian trio (9)
I believe the answer is:
trattoria
'italian eatery' is the definition.
(I've seen this in another clue)
'up tart to victorian trio' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'victorian trio' becomes 'ria' (I am not sure about this - if you are sure you should believe this answer much more).
'tart' backwards is 'trat'.
'trat'+'to'+'ria'='TRATTORIA'
'serves' is the link.
Can you help me to learn more?
(Other definitions for trattoria that I've seen before include "Place to eat" , "Italian eating establishment" , "Italian restaurant" , "where Italians eat" .)