Sweet Potato Spoon Bread

Name: Sweet Potato Spoon Bread
Ingredients: 1 pound sweet potatoes; 2 1/4 cups stone-ground yellow cornmeal, plus more for dusting; 1 1/2 tablespoons sugar; 1 1/2 teaspoons salt; 1 1/2 teaspoons baking soda; 1 1/2 tablespoons unsalted butter, at room temperature; 3 cups boiling water; 1 1/2 cups buttermilk; 1 1/2 tablespoons mild honey; 1/4 teaspoon ground cumin; 1/4 teaspoon freshly ground white pepper; Scant 1/8 teaspoon ground cloves; 1/8 teaspoon cayenne pepper; 5 large egg whites, at room temperature