Preheat the oven to 225°F (110°C) and position a rack in the center of the oven.
Meanwhile, in the bowl of a small food processor, combine the 4 large garlic cloves, 2 tablespoons fresh rosemary leaves, 2 tablespoons chopped fresh sage leaves, 1 oil-packed anchovy fillet (if using, and I hope you are), and 3 tablespoons extra-virgin oil and process until a coarse paste forms. (Alternatively, you can use a mortar and pestle.)
If desired, use kitchen string to tie the 2 pounds boneless center-cut pork loin tightly crosswise about every 2 inches (5 cm). Slip the 2 bay leaves under the twine. If you're not tying your pork, but want to use the bay leaves, carve a couple of slits in the pork and tuck the bay leaves into the slits.
Season the pork on all sides with about 3/4 teaspoon kosher salt, rubbing the meat to coat it.
In a large ovenproof skillet over medium-high heat, heat the remaining 2 tablespoons oil until shimmering. Add the pork and sear, starting with the fatty side and using tongs to turn it, until dark golden brown on all sides, 8 to 10 minutes total. Turn off the heat and let the pork in the skillet.
Using an offset spatula or pastry brush, coat the pork with the herb mixture. If you’re the sort who likes the punch of raw garlic, reserve 1 tablespoon of the herb mixture to coat the pork after it comes out of the oven.
Transfer the skillet to the center rack in the oven and roast until the meat is tender and the internal temperature is around 180°F (82°C), 2 to 3 hours. (Rest assured, if you just got alarmed at those numbers, that although this is a much higher internal temperature than we typically cook pork, it works.)
Remove the skillet from the oven. If desired, brush the top and sides of the pork with the reserved 1 tablespoon herb mixture. Let the pork cool for at least 5 minutes.
Transfer the pork to a cutting board, reserving the cooking juices in the skillet. Remove and discard the string and bay leaves, if using.
Slice the pork very thinly (about 1/8 inch | 4 mm thickness) and arrange the slices on a serving platter. Drizzle with the juices and herbs from the pan. Serve warm or at room temperature.