- 2 large white sweet potatoes (about 2 pounds total)
- 1/2 cup mirin (sweet Japanese rice wine)
- 2 tablespoons honey
- 1 tablespoon distilled white vinegar
- 1/2 teaspoon kosher salt
- 2 teaspoons corn oil
- 2 tablespoons unsalted butter
- Coarse sea salt (preferably Maldon)
- Ingredient info: Mirin is available in the Asian foods section of some supermarkets and at Japanese markets.
- Preheat oven to 450°F. Place a well-seasoned 8″-10″ cast-iron skillet in oven.
- Pierce potatoes in several spots with a fork. Microwave sweet potatoes on high for 5 minutes. (Alternatively, wrap sweet potatoes in foil and bake at 450°F until tender around edges but still hard in center, 30-35 minutes.) Transfer potatoes to a large bowl and cover with plastic wrap. Let sit for 5 minutes.
- Whisk mirin, honey, vinegar, and salt in a medium bowl. Peel sweet potatoes and cut crosswise into 1″-1 1/2″-thick rounds. Add to mirin mixture; toss to coat.
- Using oven mitts, carefully remove heated skillet from oven; add oil and swirl pan to coat. Add sweet potatoes and mirin mixture to skillet, arranging potatoes cut side down. Bake until sweet potatoes are caramelized on one side, 15-20 minutes. Turn sweet potatoes, rotating them around pan to avoid hot spots, and cook until tender and caramelized, 5-7 minutes longer.
- Transfer sweet potatoes to a platter. Add 2 tablespoons water to skillet, scraping up browned bits. Add butter, swirling pan to melt and combine. Pour sauce over sweet potatoes. Season with salt.