1. Remove filmlike silverskin from surface of tenderloin. Cut tenderloin crosswise into 12 medallions, each about 1 in. thick. Season with salt and pepper.
2. Set a large plate next to the stove. Heat oil in a very large pan (not nonstick) over medium-high heat. Add garlic and thyme; cook, stirring constantly, until garlic is browned all over, about 1 minute. Transfer to plate. Add pork and cook until well browned underneath, about 3 minutes. Turn over and cook until barely pink in the center, 1 1/2 to 2 minutes. Transfer to plate of garlic and thyme.
3. Put butter in pan and let melt. Add endive, cut sides down, and cook until browned underneath, 1 1/2 to 2 minutes. Turn over and cook 1 minute more. Transfer to plate of pork.
4. Add orange juice and maple syrup to pan and cook, scraping up browned bits, until liquid is reduced by half, about 2 minutes. Add heavy cream and boil, stirring, until thickened and reduced by half, 2 to 3 minutes.
5. Return garlic, thyme, pork, endive, and any accumulated juices to pan and heat, gently stirring, until everything is warmed through, about 1 minute. Sauce should be reduced enough to thickly coat the back of a spoon and yield about 1/2 cup.
6. Divide pork and endive among 4 plates. Spoon on sauce; garnish with parsley.