Melt butter in bottom of 9 x 13 glass dish cover with croutons in a single layer. Sprinkle with cheese and then ham. Beat egg, add salt, pepper, mustard, onion salt and milk, mix well. Pour egg mixture over dish contents cover and refrigerate 12-24 hours. Remove cover and bake 45 min at 350 degree. Let set 10 min before serving = 10-12 To freeze: prepare as directed but freeze before the soaking time.. it will soak as it defrosts. Then bake as directed.