Camélia’s Sweet Potato Gratin

Method

1. 1

   Cook 1 dried bay leaf and 3 lb. Japanese sweet potatoes (about 4 large or 6 small) or other sweet potatoes, peeled, cut into 1" pieces, in a large pot of boiling salted water until potatoes are fork-tender, 20–25 minutes. Drain, reserving 1 cup cooking liquid; discard bay leaf. Set aside; reserve pot.

2. 2

   Meanwhile, place a rack in upper third of oven and preheat to 400°. Lightly coat an 8x8" baking dish or 1½-qt. oval baking dish with unsalted butter. Stir together 2 Tbsp. white miso, 1 Tbsp. honey, and 8 Tbsp. unsalted butter, room temperature, in a small bowl until smooth. Transfer 1 Tbsp. miso butter to another small bowl; set aside.

3. 3

   Melt 2 Tbsp. (heaping) miso butter in reserved pot over medium heat. Add 1 medium shallot, halved, thinly sliced, and 3 small sprigs thyme, leaves picked; cook, stirring often with a heatproof rubber spatula, until shallot is softened, about 4 minutes. Remove pot from heat. Add reserved sweet potatoes and remaining miso butter from first bowl (a little less than 5 Tbsp.) and toss to coat. Mash sweet potatoes with spatula, adding a splash of sweet potato cooking liquid as needed, until mostly creamy with some intact pieces remaining (think halfway to mashed potatoes). Season with salt and freshly ground pepper.

4. 4

   Spread sweet potato mixture into an even layer in prepared dish. Top with 2 oz. Fontina cheese, coarsely grated (about ½ cup), and 2 oz. Gruyère, coarsely grated (about ½ cup); dot with dollops of reserved 1 Tbsp. miso butter. Bake until cheese is melted, 15–20 minutes.

5. 5

   Heat broiler (you can leave gratin in oven). Broil just until cheese is melted and browned in spots, 1–2 minutes. (Watch carefully as the cheese can go quickly from browned to burnt.) Remove gratin from oven; sprinkle aonori (dried powdered seaweed) or crushed seasoned toasted nori snacks and thinly sliced chives on top.

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