Preheat oven to 475 degrees F.
Thin the yogurt with water to make 1 3/4 cup.
In a mixing bowl, combine the dry ingredients and mix well.
In another bowl, combine the thinned yogurt and egg whites, beat till well blended, then add it to the dry ingredients and mix the bater till blended thoroughly.
Place the oil in a 9" iron skillet and heat till the oil is hot.
Pour the oil into the batter, stir well, and pour the batter back into the skillet.
Bake in the oven till the cornbread is golden brown, about 20 minutes.
To serve, turn the skillet upside down on a big plate, remove, and cut the cornbread into wedges.
(To prepare for Cornbread dressing, cool, cut into wedges and freeze until ready to use in recipe. Defrost before continuing.).