Sweet Potato Waffles

Name: Sweet Potato Waffles
Ingredients: 2 cups peeled, 1/2 cubes red-skinned sweet potatoes; 1 cup whole milk; 2 large egg yolks; 1/4 cup (packed) light brown sugar; 1/4 cup (1/2 stick) unsalted butter, melted; 1 teaspoon freshly grated peeled ginger; 1 3/4 cups all-purpose flour; 1 tablespoon baking powder; 1 1/4 teaspoons ground cinnamon; 1/2 teaspoon salt; 1/4 teaspoon ground cloves; 1/8 teaspoon freshly grated nutmeg; 6 large egg whites, room temperature; Nonstick vegetable oil spray