Pour milk in double boiler.
Stir in 1/4 cup butter, salt and grits.
Cook for about 10 minutes or to thick mush over simmering water, stirring constantly.
Beat with electric mixer for 5 minutes.
Pour into flat pan; chill.
Slice; place in casserole in overlapping layers.
Melt 1/3 cup butter; spoon over grits.
Sprinkle cheeses over top.
Bake at 400 degrees for about 30 minutes.