Fast, table d’hôte initially unavailable as ordered (2,3,6)
I believe the answer is:
at the double
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for at the double that I've seen before include "Able (to do something)" , "Pronto" , "Without delay" , "Where darts player aims to finish" , "Quickly" .)