The reverse sear technique is pretty straightforward. You cook the meat slowly, at a lower temperature, until it approaches the target temperature, perhaps within about 10 degrees Fahrenheit. The slow cook causes the heat to penetrate slowly, without overcooking the outside layers.
After that, you quickly cook the outside at high temperature to finish it off. The outside gets well-browned (potentially crispy, if there’s fat, or even crunch if you overdo it…) and really tasty, while not being there long enough to inflict much more heat on the inside.
For beef, this usually means I cook at about 225F until internal temperature reaches 120F-125F, then remove from the heat and let it rest while I get everything as hot as I can. In my case, that usually means adding more charcoal and getting that cranked up.
I then sear all sides until well-browned and juices are bubbling, then remove from the heat and let it rest (usually while I take a shower, smoke sticks to me like you wouldn’t believe).
When done properly, you can get a consistent internal cook (and color) but still get a good finish on the outside.
This is a rib eye steak I cooked last summer using the reverse sear technique. It was about an inch and a half, maybe a bit more when I was done… and as tender as anyone could ask.