Preheat the oven to 450°F.
Trim the tenderloin of any fat, cut it in half if necessary so that it will fit in your pan, and rub it with the thyme, salt, and pepper.
1 pork tenderloin, 1 teaspoon dried thyme, ½ teaspoon salt, ¼ teaspoon black pepper
In a cast iron pan or other oven-safe skillet, heat the butter or oil.
1 tablespoon butter or olive oil
When the butter or oil is hot, add the tenderloin. Brown it for a few minutes on one side, then use tongs to turn the tenderloin and brown the lateral sides for a minute. Leave it in the pan with the side you first browned face up. Turn off the heat.
Add the bourbon and brown sugar and then the apples. Stir to coat the apples and then nestle them around the pork tenderloin (but leave the tenderloin in contact with the pan).
¼ cup bourbon, 1 tablespoon brown sugar, 2 medium to large apples
Carefully move the pan to the oven and bake for about 20 to 25 minutes, until the internal temperature of the pork is 165°F. About halfway through, stir the apples once.
Remove from the oven, let rest for a few minutes, and then slice and serve the tenderloin over the apples.