Instructions
Step 1
Place the steak on a plate and pat dry if needed. Sprinkle generously with garlic salt and set aside to come up to room temperature, about 40 minutes.
Step 2
Meanwhile, in an electric spice grinder, process the rice until finely ground. In a medium skillet over medium-high heat, toast the rice powder, stirring continuously, until deep golden brown and fragrant, about 5 minutes. Turn the heat to medium-low, add the mirin and sake, and bring to a boil, stirring to loosen any browned bits from the bottom of the pan. Add the shoyu, brown sugar, vinegar, garlic, scallions, and ginger, then turn the heat to low to maintain a gentle simmer. Cook until thickened and slightly reduced, 10–12 minutes. Using a slotted spoon, remove and discard the aromatics.
Step 3
Prepare a grill for high indirect heat: For a charcoal grill, push the coals to one side; for a gas grill, leave one or two burners off. Using tongs and an oiled kitchen towel or paper towels, oil the grates. Sprinkle the steaks generously with black pepper and place on the grill on the indirect heat side. Cover the grill and cook, flipping occasionally, until a thermometer inserted into the thickest portion of the steak reads 104°F, 20–25 minutes.
Step 4
Once the meat thermometer reads 104°F, move the steaks over the direct heat. Brush the meat liberally with the reserved sauce, and grill, flipping and basting with the sauce every 30–60 seconds, until a lightly charred glaze has developed and the internal temperature reads 125°F (for medium-rare), 10–15 minutes.
Step 5
Transfer the steaks to a cutting board and set aside to rest for 10 minutes. Carve against the grain into thick slices and serve immediately with the remaining sauce on the side.