Experience Cache

First craft a Golden gem (Emerald, Diamond, or Nether Star)

Then cook it in a furnace to transform it

Craft the Experience Cache Block

Place the cache block somewhere in your world and right click on it while holding an XP gem to insert the gem.  The block can only hold one gem at a time.

Sneak right click on the cache block with an empty hand to deposit all of your XP.

Right click on the cache block with an empty hand to extract 1 level of XP.

Sneak left click on the cache block with an empty hand to take out the gem.