Twinkle, sparkle (11)
I believe the answer is:
scintillate
I believe this clue is a double definition.
'twinkle' is the first definition.
(I know that twinkle can be written as scintillate)
'sparkle' is the second definition.
(to scintillate is to sparkle or gleam)
(Other definitions for scintillate that I've seen before include "Emit flashes of light" , "give sparkling performance" , "Twinkle - sparkle" , "Coruscate" , "Glitter" .)