From The Modern Family Cookbook
2½ squares (2½ oz.) baking chocolate
½ cup sugar
6 tablespoons flour
¼ teaspoon salt
1â…” cups evaporated milk
¾ cup water
12 marshmallows, quartered
1 egg, well-beaten
1 teaspoon vanilla

Melt chocolate over hot water in top of double boiler. Thoroughly mix the sugar, flour and salt; add to chocolate and stir until well blended. Add about ¼ cup of the milk, stir to a smooth paste and stir in the rest of the milk and the water. Cook until thickened, stirring constantly. When thick, add the marshmallows, cover and continue cooking 15 minutes with occassional stirring. Stir a little of the hot mixture into the beaten egg and return to double boiler for 2 minutes, stirring all the time. Then remove from heat and add vanilla. Serve warm or cold with milk or cream. 5 servings.
My note: Have I mentioned I really need a double boiler? I do.