1. Preheat the oven to 375°. With a fork, pierce the sweet potatoes all over and set them directly on the oven rack. Bake the sweet potatoes for 1 hour, or until they are tender; let cool slightly. Slit the skins and scoop the potatoes into a large bowl. Mash until smooth. You should have 1 1/4 cups of mashed sweet potatoes. Increase the oven temperature to 425°.
2. Meanwhile, lightly butter a shallow 2-quart glass or ceramic baking dish and dust it with cornmeal, tapping out any excess. In another large bowl, whisk the cornmeal with the sugar, salt and baking soda. Melt the butter in the boiling water, then stir the butter-and-water mixture into the dry ingredients. Let cool slightly.
3.Using an electric mixer, beat the buttermilk, honey, cumin, white pepper, cloves and cayenne into the mashed sweet potatoes until combined. At medium speed, beat in the cornmeal mixture.
4. In a clean stainless steel bowl, using clean beaters, beat the egg whites until stiff but not dry. Fold the beaten egg whites into the sweet-potato mixture until no white streaks remain. Pour the batter into the prepared baking dish and bake for about 40 minutes, or until golden and risen and a toothpick inserted in the center comes out clean. Serve the sweet potato spoon bread warm or at room temperature.
The best part of this recipe is the spoon bread can be made early in the day, wrapped in foil and reheated in a 350° oven.