... How do you do a time-skip? ... Or really, how do you do a middle when the middle is unnecessary?

I have a deeply relevant beginning. I have a very relevant ending.
The middle in between... Is unimportant. I know what happens during it, and a large amount of time should pass in said middle, but it's so unimportant to the actual story that the only reason I'd write it would be that the shift between beginning and ending won't be so jarring. It's an odd problem. I wrote my beginning first, then my ending, and now I'm like... "Yeah, anything that happened between these two events are thoroughly unimportant and would just waste the reader's time". ... Hm. What to do...