Strong coffee (5)
(Other definitions for mocha that I've seen before include "Arabian coffee" , "Coffee flavour" , "Macho (anag.); coffee with chocolate" , "Fine quality coffee" , "Kid" .)
'strong coffee' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for espresso that I've seen before include "Barista's beverage" , "Steamed coffee" , "Coffee-making machine" , "Type of coffee" , "Kind of coffee made with steam" .)