This fits on a jelly roll pan (buttered). A jelly roll pan has an inch lip and measures 15 1/2 x 10 1/2 x 1.
In a large saucepan, mix together chocolate bits, marshmallow, vanilla, margarine, and nuts (optional). Set aside.
In a second saucepan, boil evaporated milk, salt and sugar. Boil over medium heat. Once it starts to boil, keep boiling and stirring for 15 minutes. Stirring must be constant. If you have a candy thermometer when it comes to 234 degrees it's ready.
Remove from heat and pour into the mixture in other saucepan. Stir until everything is melted and smooth. Pour into the jelly roll pan. Let cool and cut into squares.
Makes 5 pounds of fudge.