This Grilled Tomahawk Ribeye is reverse-seared for a smoky, juicy center and a beautifully seared crust. It's served with tender cast-iron potatoes topped with sautéed onions and plenty of melted smoked Gouda.
Remove the Tomahawk ribeye from the refrigerator and let it sit at room temperature for about 40 minutes. Pat it completely dry with paper towels.
Combine the kosher salt, smoked paprika, garlic powder, Mexican chili powder, onion powder, and black pepper in a small bowl.
Lightly coat the steak with avocado oil, then generously season the entire surface with the dry rub.
Use a mandoline to cut the potatoes into thin round slices.
Brush the bottom of a cast-iron skillet with duck fat. Arrange the potato slices in a spiral pattern and season with some of the remaining dry rub. Cover the skillet with aluminum foil.
Preheat the smoker to 275°F. Place both the Tomahawk steak and covered skillet of potatoes on the smoker.
Cook the potatoes for 45–50 minutes, or until tender when pierced. Smoke the steak until it reaches an internal temperature of 118–120°F.
While the steak and potatoes cook, heat a skillet over medium-low heat. Add some of the duck fat and the sliced yellow onion. After a few minutes, add the butter.
Cook the onions for 20–25 minutes, or until softened and sautéed. Keep warm.
Remove the steak from the smoker when it reaches 118–120°F. Let it rest on a wire rack while preparing the grill for direct high-heat searing.
Sear the steak over very hot coals for 60–90 seconds per side.
Remove the steak and let it rest on a wire rack for 12 minutes.
Remove the foil from the potatoes and top them with the shredded smoked Gouda and sautéed onions.
Return the skillet to the grill for about 5 minutes, or until the cheese is completely melted.
Slice the rested steak and serve with the cheesy cast-iron potatoes.