In a small pot or a microwave-safe bowl combine the bourbon, brown sugar, soy sauce. Heat over low heat for a few minutes, stirring often, until the brown sugar is dissolved – or do this in the microwave, working in 20-second bursts. Stir in the Worcestershire sauce, lemon juice, thyme and pepper. Allow to cool completely.
Place the marinade in a large sturdy zipper top bag or a container big enough to hold the meat. Add the marinade and turn the pork to coat well. Cover, and place in the fridge to marinate overnight, or at least 6 hours.
Preheat the oven to 425ºF. Cover a rimmed baking sheet or a baking pan with foil, wrapping it well to enclose the whole pan (see recipe intro). Place the pork on the baking sheet or pan, and roast for about 15 to 30 minutes (it really depends on the thickness of the pork loin), until a meat thermometer registers 145ºF. If you have the inclination, baste it after 10 minutes with any extra marinade. Let the pork sit on a cutting board for 10 minutes before slicing it.