Preheat oven to 375°. Spray a 13x9-inch baking dish with cooking spray.
In a large skillet, melt 2 tablespoons butter over medium-high heat. Add pears, cut side down, and cook until lightly browned, about 2 minutes. Remove pears from skillet. Sprinkle pork with salt and peppers. Add to skillet, and cook until browned, about 4 minutes, turning occasionally.
Place pears, cut side down, and pork to prepared dish; brush with vinegar. Sprinkle pork with sage and thyme. Cut remaining 2 tablespoons butter into small pieces and sprinkle over pork and pears.
Bake until a meat thermometer inserted into the thickest portion of pork registers 145° and pears are tender, about 18 minutes. Lightly cover and let stand 10 minutes before serving. Serve with pan juices. Garnish with sage and thyme sprigs, if desired.
Notes *Slightly unripe pears work best in this recipe. Fully ripe pears can become too soft when cooked.