what is a "reverse sear"?

I explained the concept of reverse searing once before, but I'll do it here again. Traditionally, people cooking steaks would first sear the steak, allowing the outside to cook super-rapidly and develop a healthy crust. They would then finish the steak in the oven, cooking it to proper doneness. With a reverse sear, you cook the steak to doneness first, then do the sear as the last step. Sous vide allows you to control the temperature of the cook, and it ensures an even, edge-to-edge doneness to the steak. You then take the done steak out of the sous-vide water bath and sear it in a ripping-hot pan (in cooking videos, these pans are always described as "ripping hot"). This rapidly creates a crust via the Maillard reaction, which is what happens when you expose sugar and protein to heat (this is why bread browns when you bake it), producing a savory layer of flavor. Voilà: a done steak through a successful reverse sear! Just make sure not to leave the steak on the hot pan for too long, or your sous vide will have been in vain as all the meat proteins seize up, and you end up with a tough hunk of flesh.

Now, go forth and reverse sear!