In a small, nonporous bowl, combine the peppercorns, tamari, garlic, sugar and salt. Add the beef filet and coat well on all sides. Cover and marinate in the refrigerator for 1 hour.
Melt butter in a medium saucepan over medium high heat. Place the beef filet in the pan and saute for 6 to 8 minutes per side, or until internal temperature reaches at least 145 degrees F (65 degrees C).