Heat the oil in a large Dutch oven (or similar, heavy-bottomed pan) over medium-high heat. Saute the pork for about 5 minutes on each side, then remove it to a plate. In the same pan over medium heat, saute the garlic, rosemary and sage, stirring, for about one minute. Add the wine to the pan and use a wooden spoon to scrape the bottom of the pan. Cook the wine until the smell of the alcohol has disappeared, about 1 to 2 minutes.
Lower the heat under the pan to low-medium heat. Return the pork to the pan and season with salt and pepper. Partially cover with a lid and cook for about 1 1/2 hours (considerably less if you're using pork tenderloins instead. Rely on a thermometer to check for doneness), flipping the pork and scraping the bottom of the pan every 20 minutes or so. Keep an eye on it, making sure there continues to be some liquid in the pan. Add 1/4 cup of warm water if necessary.
When the pork is cooked through (ideally, you want to test with a thermometer, it should be about 140°F internal temperature.) Remove pork to a cutting board to rest and cover with loosely with a sheet of aluminum foil to help retain the heat while it rests.
Meanwhile, increase the heat under the liquid in the pan to medium. If your pan has little liquid, deglaze with a splash of white wine. Stir well to loosen the browned bits on the bottom of the pan. Allow to cook until the alcohol smell disappears (about 1-2 minutes). Add the chicken stock and stir to combine. Heat over medium heat a few minutes, to allow the chicken stock to heat through a bit. Reduce heat to medium-low. Add the cream. Heat gently over medium-low heat, stirring the sauce constantly, until it thickens a bit and is warmed through. Avoid vigorously boiling. A gentle simmer is fine. (*If your sauce doesn't thicken up, mix 2 Tbsp. cornstarch with 2 Tbsp. water and add a bit at a time to your sauce until it thickens to your liking.) Taste sauce and add salt and freshly ground pepper, to taste.
When the sauce is ready, slice the pork very thinly and place on to a serving platter. Pour the warm gravy over-top to serve.
Note that this recipe is best made with a pork loin roast, not a pork tenderloin. Pork tenderloins are considerably thinner and cook much more quickly. As such, you won't get the benefit of the low and slow cooking or the flavours that comes from cooking a larger roast.
Be sure to read the "Cook's Notes" in the original post, for more tips, options, substitutions and variations for this recipe!