1. Combine cornmeal, flour, baking powder, sugar, and salt. Mix well.
2. Smoothly blend buttermilk, eggs, and egg whites in a separate bowl.
3. Add the buttermilk mixture to the cornmeal mixture and stir just until combined. Do not overmix.
4. Spread the batter in a lightly oiled baking pan or half sheet pan. Bake in a moderate (350°F/175°C) oven until bread pulls away from sides of pan and a wooden skewer inserted in the center comes out clean.
5. Slice as desired.