Instructions

Combine the 2 cups mashed cooked sweet potatoes, 1 cup milk, 2 large egg yolks, ¼ cup packed light or dark brown sugar, and 4 tablespoons melted unsalted butter in a large bowl. Use a fork or whisk to blend until the mixture comes together. (It’s OK if there are a few stubborn bits of sweet potato.)
Add the 1¾ cups all-purpose flour, 1 tablespoon baking powder, 2 teaspoons ground cinnamon, ½ teaspoon ground ginger, ½ teaspoon kosher salt, and ¼ teaspoon ground nutmeg. Stir until it comes together; the mixture will be paste-like, heavy, and dense.
In another large bowl, use an electric mixer on medium speed to whip 6 egg whites until stiff peaks form, about 3 minutes. Use a silicone spatula to stir one-third of the whipped whites into the batter to lighten it. Once the egg whites are incorporated, fold in the remaining two-thirds until no streaks of the egg whites remain, about 30 seconds.
Heat a waffle iron. When ready, coat the iron with a little butter, oil, or cooking spray. Pour about ½ cup of the batter into the center of the iron and sprinkle 1 or 2 tablespoons of the pecans (if using) on top. Close the lid and cook according to the manufacturer’s directions, until the waffle is cooked through and golden brown. Repeat until all the waffles are cooked. Serve warm.