Skill, in short, needed to make a cocktail (7)
I believe the answer is:
martini
'a cocktail' is the definition.
(I know that Martini is a type of cocktail)
'skill in short' is the wordplay.
'skill' becomes 'art' (both can mean a talent).
'in' means one lot of letters goes inside another.
'short' becomes 'mini' (similar in meaning).
'art' put into 'mini' is 'MARTINI'.
'needed to make' acts as a link.
(Other definitions for martini that I've seen before include "Alternative name for Simone Memmi, pre-Renaissance Italian painter" , "In glass, one's dry" , "Cocktail of gin and dry vermouth" , "Sienese painter" , "Type of Italian vermouth" .)