Mix bread cubes, cheese, and butter.
Add egg yolks, beaten well with a fork. Add salt.
Heat the milk to scalding; do not boil.
Pour milk over the ingredient mixture and mix well.
Beat egg whites until very stiff and fold into mixture until blended.
Pour into a small casserole that has been greased with butter to prevent sticking.
Bake at 350° for 35 minutes.