Tia Maria, that's right good for one mixing cocktail (9)
I believe the answer is:
margarita
'cocktail' is the definition.
(I know that Margarita is a type of cocktail)
'tia maria that's right good for one mixing' is the wordplay.
I cannot quite see how this works, but
an anagram of 'tia' is 'ita' which is located in the answer.
'right' could be 'ar' (I've seen this in other clues) and 'ar' is found within the answer.
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
'one' could be 'a' (a thing is one thing) and 'a' is found within the answer.
The remaining letters 'mr' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for margarita that I've seen before include "Stiff drink" , "Tequila/citrus cocktail" , "Tequila and lime cocktail" , "Caribbean island" , "Spanish girl" .)