Makes: 12 pieces. Prep: 15 minutes. Bake: at 375° for 30 minutes
Heat oven to 375°F. Put the butter in an 8-inch-square baking pan over medium heat; heat until hot, about 2 minutes, then turn off the heat. Meanwhile, combine cornmeal, flour, baking powder, salt and sugar in a bowl. Mix egg yolks into the buttermilk. Stir the liquids into the cornmeal mixture, combining well.
Beat egg whites until stiff but not dry; gently stir into batter and pour into prepared pan. Bake at 375°F for about 30 minutes, until the top is lightly browned and a toothpick inserted into the center comes out clean. Serve hot or warm.