Someone needs to learn to release the handbrake only once the clutch starts biting in...

First time _reversing_ on a slope.

Same principles, same technique. Like I said, one fluid motion. You're doing the forward bits more or less fine now (just need polishing), just need to apply exactly the same technique going backwards. At the moment you're still doing the "look backwards, release handbrake, rev up, pause, pause, pause, release clutch" thing.

 

It'll come with practice.