Place roast into a shallow, glass baking dish. Pour soy sauce and melted butter over the tenderloin.
Bake in preheated oven for 10 minutes, then turn the roast over, and continue cooking 35 to 40 minutes, basting occasionally until the internal temperature of the roast is at 140 degrees F (60 degrees C) for medium. Or, cook to your desired degree of doneness. Let meat rest for 10 to 15 minutes before slicing.