Regularly lap up brandies with which to greet the dawn (6)
I believe the answer is:
aubade
'with which to greet the dawn' is the definition.
(type of poem composed about dawn)
'regularly lap up brandies' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'lap'+'up'+'brandies'='lapupbrandies'
The alternating letters of 'lapupbrandies' are 'AUBADE'.
(Other definitions for aubade that I've seen before include "Piece of music appropriate to the dawn" , "Festive occasion" , "Early announcement" , "Sunrise song" , "Morning song" .)