Dramatic beginning formulated at once (3,3)
I believe the answer is:
act one
'dramatic beginning' is the definition.
(I've seen this before)
'formulated at once' is the wordplay.
'formulated' indicates anagramming the letters.
'at'+'once'='atonce'
'atonce' with letters rearranged gives 'ACT ONE'.
(Other definitions for act one that I've seen before include "First major segment of a play" , "Dramatic beginning" , "Bit of drama" .)