Sweet drink chasing first of bitters, say (12)
I believe the answer is:
butterscotch
'sweet' is the definition.
(butterscotch is a kind of sweet)
'drink chasing first of bitters say' is the wordplay.
'drink' becomes 'scotch' (Scotch is an example).
'chasing' says to put letters next to each other (some letters chase after others).
'first of' says to take the initial letters.
'say' becomes 'utter' (to utter something is to speak or say it).
The first letter of 'bitters' is 'b'.
'b'+'utter'='butter'
'scotch' after 'butter' is 'BUTTERSCOTCH'.
(Other definitions for butterscotch that I've seen before include "Kind of toffee" , "Hard brittle toffee" , "Type of toffee" , "confectionery" , "Brittle, yellow-brown sweet" .)