Drain the pork and pat dry with paper towels.
In a small bowl (or using a mortar and pestle), crush together the olive oil, salt, pepper, rosemary and sage into a paste. Rub the pork loin with the paste and place in a foil lined roasting pan or a foil lined rimmed baking sheet.
Position a rack in the center of the oven and preheat oven to 450 F.
Allow the pork loin to sit out at room temperature while you are preheating the oven.
Add the carrots, celery and onion pieces around the pork in the roasting pan.
Roast pork and vegetables uncovered for 35-45 minutes (until the pork begins to brown), then add the white wine.
Reduce the heat to 350 F and continue cooking uncovered until an instant-read thermometer inserted into the thickest part of the loin reads 145 F., about 40 to 50 minutes more. Your meat thermometer should read 145°F (63°C). You may need to adjust the cooking time, depending on the weight of the pork roast. (It takes about 22 minutes per pound for medium done. For pork more well-done, cook it for 27 minutes per pound.)
Remove from oven and let rest for 10 minutes. Don't cover the roast while it's resting. While the pork is resting, prepare the sauce.
Puree the vegetables and the juices that were in the roasting pan with an immersion blender (or in your blender) with the broth. If you don't have any broth on hand, you could even add a little water. Heat the sauce on medium-low before serving with the butter. Stir together and let it simmer a few minutes until nicely combined. Check the salt, and add more if necessary to the sauce. Thinly slice the pork and serve it with the sauce and mashed potatoes (or even polenta).