Preheat the oven to 325°F.
Pat the pork loin dry with a paper towel and season with salt and black pepper.
Heat the olive oil in a Dutch oven over medium-high heat.
Sear pork for 2–3 minutes per side, until golden brown.
Transfer the pork to a cutting board and reduce the heat to medium.
Add the mushrooms and onion. Cook for 3–4 minutes.
Add the garlic and cook for another 30 seconds.
Pour in the wine and scrape the browned bits from the bottom of the pan.
Add the chicken broth and Worcestershire sauce. Return the pork to the pot.
Cover with a tight-fitting lid and transfer to the oven.
Braise for 45–60 minutes, or until the internal temperature reaches 145°F.
Transfer the pork to a serving platter, loosely cover with aluminum foil, and let it rest for 10–15 minutes.
Place the Dutch oven over medium heat and simmer the braising liquid until slightly reduced.
Melt the butter into the pan sauce, then slice the pork and serve with the mushrooms and gravy.