Cut cheese into small pieces and melt in double boiler. When melted, add evaporated milk, salt and mustard. Remove from heat and stir in eggs. Return to double boiler and stir and cook until eggs thicken sightly. Remove from heat. Pour into a dish and cool slowly. Stir as it cools to prevent a crust from forming. (Might just be able to cover with plastic wrap, too.) Put in jars, cover and store in refrigerator. Keeps several weeks.