Combine cornmeal and scalded milk in top of double boiler, mixing well. Stir in egg yolks and 1 cup milk. Place over boiling water; cook, stirring constantly, until mixture reaches the consistency of mush. Remove from heat, and stir in butter, baking powder, and salt.
Beat egg whites (at room temperature) until stiff peaks form; fold into cornmeal mixture. Spoon into a greased 2-quart casserole. Bake at 400° for 35 minutes or until a knife inserted in center comes out clean. Serve immediately.