The explanation for these is simple, but they're far from easy. Do a close-grip chin-up as slowly as you can. That's it.
Shoot for 20-30 seconds on the concentric (going up) and 30-40 seconds on the eccentric (coming down) to start. If you can do that, add some weight. If that's too much, then just go as slowly as you can. I also like to do a static hold at the top.
Use a supinated grip for more biceps emphasis or a neutral grip to target the brachialis. Either way, it'll also blast your forearms and help build tremendous grip strength.
Save this for the tail-end of your workout and just do one painstaking rep. If you're doing it right, that's all you'll be able to muster.