Heat the oil in a large Dutch oven over medium-high heat. Sauté the garlic, rosemary and sage, stirring, for about one minute. Add the pork loin to the pan, carefully placing it on top of the herbs. Sauté the pork for about 5 minutes on each side, then remove it to a plate. Add the wine to the pan and use a wooden spoon to scrape the bottom of the pan. Cook 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 (probably less if you're using a pork tenderloin), 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 (if you want to test with a thermometer, it should be about 150° internal temperature) remove pork to a plate to rest. Meanwhile, increase the heat under the liquid in the pan to medium. If your pan has very 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. Remove pot from heat and allow to cool in the pot for 20 minutes.
When the sauce has cooled, add the cream and put the pan back on the stove. Heat gently over medium-low heat, stirring the sauce constantly until it thickens a bit and warms. Avoid boiling. (*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.
Place the resting pork on a cutting board (you can add any accumulated meat juices back to the sauce if you like!). Slice the pork thinly and place onto a serving platter. Pour the warm gravy over top.