Stir the boiling water into cornmeal in a bowl, then cool slightly.
Add the butter and egg yolks and stir until thoroughly blended.
Stir in the buttermilk, sugar and soda.
Beat the egg whites until soft peaks form, then fold into cornmeal mixture.
Pour into a greased 2-quart casserole.
Bake in 375-degree oven for 45 to 50 minutes.
Serve hot with butter.