Build a wood fire in your grill with a hotter fire on one side and a smoldering smoky fire on the other side. Set a grill grate high above the heat.
Season the steaks on both sides with salt and pepper, then drizzle with olive oil. Use the flat of a table fork to pat in the seasonings.
Arrange the steaks on the grill grate and smoke for about an hour over the cooler part of the fire, turning once. The internal temperature of the steaks should not exceed 100 degrees. If you see the steaks are cooking too quickly, move them away from the heat.
Meanwhile, make the jalapeño horseradish butter. Place the butter (make sure it’s at room temperature) in a mixing bowl. Using a wooden spoon, stir in the jalapeños, horseradish, and parsley. Spoon the butter onto a large sheet of plastic wrap. Roll it up into a cylinder about 6 inches long and 1 1/2 inches in diameter. Chill the resulting butter in the freezer until firm, then transfer to the refrigerator.
Once the steaks are smoked, transfer them to a wire rack over a sheet pan. Set up your grill for direct grilling and have one zone on high and one zone on medium. Arrange the steaks on the grill and grill until sizzling, browned, and cooked to taste: 130 degrees for medium-rare. Depending on the internal temperature when you start, you may be able to do all the grilling over the hot zone. Or if the outside of the steak browns too much before the inside is cooked, slide the steaks over the medium zone to finish cooking.
Transfer the steaks back to the wire rack over the sheet pan and let rest for 2 minutes. Unwrap and cut the jalapeño horseradish butter crosswise into 3/4 inch thick disks. Transfer the steaks to a platter or plates and place a slice of the butter atop each. Using a blowtorch or a hot ember held at the end of tongs, partially melt the butter onto the steaks.
Serve at once with smashed potatoes on the side.
Smashed Potatoes
Wrap the potatoes and 3 tablespoons butter in heavy duty foil. The potatoes should be in a single layer. Arrange the resulting packet directly on the coals. Cook the potatoes until soft (they’ll crush when pressed through the foil), turning every 5 minutes with tongs. The total roasting time will be 20 to 30 minutes. Transfer the potatoes to a sheet pan and keep warm until serving.
Just before serving, melt the remaining butter in a large cast iron skillet or on a plancha and heat until sizzling. Unwrap the potatoes and place in the skillet. Flatten with a grill press, the back of a small skillet, or a potato masher. Sizzle the potatoes in the hot butter until crisp and browned, 3 to 5 minutes per side, turning with tongs. Season the potatoes on both sides with salt and pepper.
