For the Sweet Potatoes
3 pounds sweet potatoes, skin on
1 cup (2 sticks) cold butter, cut into cubes, plus extra for greasing the pan
1⁄2 cup maple syrup
1 teaspoon ground ginger
1⁄2 teaspoon ground cinnamon
1⁄4 teaspoon freshly grated nutmeg
1 teaspoon kosher salt
1 teaspoon white pepper
For the Meringue
1 1⁄4 cups egg whites (from about 10 large eggs), at room temperature
1⁄8 teaspoon cream of tartar
1⁄8 teaspoon pure vanilla extract (preferably Nielsen-Massey)
3 cups granulated sugar
To make the sweet potatoes
- Preheat the oven to 350° F. Butter a 9-inch round casserole dish.
- Place the sweet potatoes on a baking sheet and bake until they are soft and give to the touch when squeezed in the center. This should take 1 to 2 hours, depending on the size of the potatoes. Peel the sweet potatoes while still warm. Place in the bowl of a food processor and puree until smooth.
- Add the butter, maple syrup, ginger, cinnamon, nutmeg, salt, and white pepper. Transfer to the prepared casserole. (You can prepare the casserole in advance up to this point; it will keep, covered in the refrigerator, for up to 2 days.) When you are ready to serve, bake the casserole for 30 minutes, until heated through.
To make the meringue
- In the clean bowl of a stand mixer fitted with the whisk attachment, beat the egg whites, cream of tartar, and vanilla. Bring to soft peaks and slowly add the sugar; the meringue should be shiny and silky—do not overwhip.
- Preheat the broiler. Top the sweet potatoes with dollops of meringue. Toast about 4 inches from the broiler for about 5 minutes, until golden brown. (Alternatively, you may toast the meringue using a propane torch: Hold the torch 5 to 6 inches from the meringue and move it in sweeping motions across the meringue until it is golden brown, being careful not to hold the flame over one place too long.) Serve immediately.