In a spice grinder, coarsely grind the peppercorns. Alternatively, crush them with a mortar and pestle or put them in a sturdy resealable plastic bag and smash them with a meat mallet or cast iron skillet.
Put the steaks in a shallow dish or on a plate. Brush the steaks with Worcestershire sauce. Season the steaks with the pepper - as much or as little as you want - pressing the pepper into both sides of the steaks with the palm of your hand. Return the steaks to the refrigerator while you start the grill.
When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes). Put a large well-seasoned cast iron skillet on the cold grill grate. Set the temperature to 400F and preheat, lid closed, for 15 to 20 minutes.
Season the steaks with coarse salt. Arrange the steaks in the skillet - you should hear them sizzle when they hit the hot cast iron - and sear for 1 to 2 minutes per side, or until nicely browned.
Carefully move the skillet with the steaks to a cooling rack near the grill, and using tongs, transfer the steaks to a clean platter or plate. (You will not need the skillet again. Move it out of the way as it will stay hot for some time.) In the meantime, lower the temperature of the grill to 225F.
Put the steaks directly on the grill grate and cook until done to your liking, about 30 minutes for medium-rare, longer for medium-well. Use an instant-read meat thermometer inserted through the side of a steak to check the internal temperature. Medium-rare will be about 135F.
Put the butter pieces on a cutting board and place steaks on top. Let the meat rest for 3 minutes before slicing and serving. (The butter will mingle with the meat juices and make the steaks more succulent.)