1. Using a mortar and pestle or the flat side of a knife, mash the garlic with 1 tsp. of the salt until it forms a paste.
2. Transfer the garlic paste to a small bowl. Whisk in the olive oil, vinegar, sage, rosemary, thyme, pepper and the remaining 1 tsp. salt.
3. Smear the mixture all over the pork. Transfer the pork to a bowl. Cover tightly with plastic wrap and refrigerate for at least 1 hour or overnight. Let the pork come to room temperature before grilling.
4. Preheat the grill to medium-high heat, and brush the grate with oil or spray with nonstick cooking spray.
5. Transfer the pork to the grill. Close the cover and cook, turning once, until a dark golden crust forms on the pork and the meat is just cooked through, 7-9 minutes per side.
6. Let the pork rest on a cutting board for 5 minutes before slicing and serving.
Tip: If you want to be sure a big piece of meat like a pork tenderloin is perfectly cooked through and nice and juicy – and you don't much care about the char – try this fail-safe method: Wrap the meat in aluminum foil and prick the foil all over to let the heat in and some of the steam out. Then grill as usual. This way, you can get a little of that smoky taste, all the convenience and easy cleanup of grilling, but less of the super-dark, unpredictable char that can make grilling a larger cut tricky.