- Build a two-zone fire in a charcoal grill by situating the coals on only one side of the grill, leaving the other side empty. Preheat the grill to 400°F.
- Wash the sweet potatoes and wrap individual in foil. Put the wrapped sweet potatoes over indirect heat, away from the coals. Close the grill lid and cook until they are soft, about 1 hour 15 minutes.
- Remove the sweet potatoes from the grill, unwrap, and stop the cooking process by dipping them into a bowl of ice water for 4 minutes. Remove the sweet potatoes from the ice water and set aside to cool for at least 30 minutes before cutting.
- For the maple pecan butter: In a small saucepan, melt the butter over direct heat. Add the maple syrup, pecans, and cinnamon. Heat the mixture until a layer of bubbles forms over the surface, less than 1 minute. Remove the pan from the heat; set aside and keep warm.
- Cut the sweet potatoes crosswise into 1/2-inch-thick medallions. Grill each steak over direct heat until they are lightly charred, about 3 minutes per side. Remove them from the grill and drizzle with the warm maple-pecan butter. Serve hot.