Cut cheese in small pieces. Melt the butter in top of a double boiler, add the onion and cook until onion is soft. Stir in the flour and blend; then gradually add the milk and mix well. Add the cheese and cook until the cheese has melted. Mix together the catsup, mustard, Worcestershire sauce, salt and paprika; add to cheese sauce and cook for 5 minutes. Stir in the egg and cook one minute longer. Serve at once on toast or crackers. Source: Pennsylvania Dutch Cook Book - Fine Old Recipes, Culinary Arts Press, 1936.