Season 5 of Christopher Kimball's Milk Street Television airs Saturdays at 3:00 pm.
Sometimes you need to reinvent the classics. We've already shared a possibility for a different kind of green bean casserole, spiced-up mashed potatoes, and pumpkin seed dinner rolls, and now we have another Milk Street recipe that could replace a Thanksgiving mainstay: sweet potato casserole. There are no marshmallows in sight in this savory sweet potato gratin. Instead the excitement comes from the complement of miso, soy, and ginger against the warm sweetness of the potatoes. You'll never think of serving saccharine sweet potatoes again.
Savory Sweet Potato Gratin
Umami-rich miso adds savoriness to this smooth sweet potato gratin spiked with fresh ginger and soy sauce. We liked mellow white miso best, which has a milder flavor than yellow or red miso. For a crispy topping, we toasted panko breadcrumbs in butter, then mixed them with sesame seeds, brown sugar, and white pepper. To make holiday-dinner prep more convenient, the gratin can be made up to a day ahead. Roast the sweet potatoes, cool them enough to peel, then make the sweet potato mixture as instructed. Transfer to a baking dish, cover with foil and refrigerate overnight. The next day, bring to room temp for 1 hour, then bake at 400°F for 50 minutes. In the meantime, make the topping. Once the sweet potatoes are warmed through, sprinkle with the topping and bake as instructed for 20 minutes.
Don't use garnet or ruby sweet potatoes (often called yams). They are too dry and won't yield the desired creamy texture. Beauregard sweet potatoes, the most common variety available at grocery stores, worked nicely. Choose potatoes that are large and bulbous rather than long and slender.
For the sweet potatoes:
5 pounds orange-fleshed sweet potatoes
2 tablespoons packed light brown sugar
2 tablespoons soy sauce
1⁄2 teaspoon ground white pepper
1 cup heavy cream, divided
6 tablespoons salted butter, room temperature, divided
1 tablespoon finely grated fresh ginger, divided
5 tablespoons white miso
For the topping:
6 tablespoons salted butter
1 1⁄2 cups panko breadcrumbs
2 tablespoons light brown sugar
2 tablespoons white sesame seeds
1 teaspoon ground white pepper
1. Heat the oven to 400°F with a rack in the upper-middle position. Pierce the potatoes all over with a fork and set on a rimmed baking sheet. Bake until the potatoes are very soft and tender, about 1 1⁄2 hours. Remove from the oven but leave the oven on. When cool enough to handle, peel the potatoes and scrape the pulp into a medium bowl. Discard the skins.
2. Transfer half of the sweet potato pulp to a food processor and add the brown sugar, soy sauce, white pepper, 1⁄2 cup of the cream, 3 tablespoons of the butter, half of the ginger, and half of the miso. Process until smooth, about 1 minute, scraping the bowl. Transfer to a large bowl. Repeat with the remaining potatoes, cream, butter, ginger, and miso. Whisk the mixture to combine, then transfer to a 13-by-9-inch baking dish and spread evenly.
3. To make the topping, melt the butter in a 12-inch skillet over medium. Add the panko and cook, stirring, until light golden brown, about 5 minutes. Transfer to a bowl and let cool for 10 minutes. Stir in the brown sugar, sesame seeds, and white pepper. Sprinkle the topping evenly over the potatoes. Bake until bubbling and the topping is golden brown, about 20 minutes. Let cool for 20 minutes before serving.