Butter the square pan lightly.

In the saucepan, combine the evaporated milk, the sugar and the salt.

Cook over low heat for five minutes, stirring constantly, until it reaches a boil. Boil gently for five minutes, stirring all the time.

Remove from heat. Add the marshmallows, chocolate chips and vanilla.

Stir until the marshmallows dissolve. Add walnuts if you want them.

Pour mixture into the buttered pan. Jiggle the pan until the fudge smoothes out.

When cool, cut into small squares and use the knife or spatula to get the pieces out of the pan.