- 1/2 cup plus 2 tablespoons olive oil
- 1/3 cup soy sauce
- 2 tablespoons mirin
- 2 tablespoons peeled and minced fresh ginger (from about a 2-inch piece)
- 1 tablespoon rice vinegar
- 2 teaspoons packed light brown sugar
- 2 medium garlic cloves, minced
- 4 pounds sweet potatoes, peeled and cut into 1-inch pieces
- 1 cup panko
- 3 medium scallions, thinly sliced (white and light green parts only)
- Heat the oven to 425°F and arrange a rack in the middle.
- Whisk 1/2 cup of the oil, the soy sauce, mirin, ginger, vinegar, brown sugar, and garlic in a large bowl until the sugar has dissolved. Add the sweet potatoes and toss to combine.
- Transfer the mixture and any liquid to a 13-by-9-inch baking dish and spread into an even layer. Cover the dish tightly with aluminum foil and roast for 20 minutes.
- Meanwhile, heat the remaining 2 tablespoons of oil in a medium frying pan over medium heat until shimmering. Add the panko and cook, stirring occasionally, until lightly browned and toasted, about 7 minutes. Remove the pan from the heat and set aside.
- Remove the potatoes from the oven and remove the foil. Toss the sweet potatoes, moving the bottom layer to the top and the top layer to the bottom (this helps the potatoes cook evenly in the glaze). Spread them back into an even layer and roast uncovered for 10 minutes. Toss again and roast until the sweet potatoes are tender and the glaze has thickened, about 10 minutes more. Sprinkle with the toasted panko and scallions and serve.