Prepare a sauce from flour and butter. Add milk all at once, then salt and pepper.
When this is thickened, add the grated cheese and stir until smooth, remove from fire and add some of this hot mixture to the slightly beaten egg yolks.
Cool and carefully fold in the beaten egg whites.
Turn into buttered baking dish, set into pan of water and bake at 425° for 10-12 minutes. This forms brown crust when done. Insert a clean knife.