Anywhere from 24 to 5-6 hours before you plan on eating trim access fat off the roast (I leave some on, though). Salt it with the tablespoon of kosher salt and set it on the wire wrack placed over a roasting pan. Put this in the fridge, uncovered. The salt dissolves, pulling out some of the natural moisture to the surface of the meat, before it reacts with the proteins and the liquid absorbs back into the meat, taking the salt with it. Don’t skip it.