Line 8-inch (2 L) square baking pan with waxed paper; set aside
Combine sugar, evaporated milk, butter and salt in medium saucepan; bring to rolling boil over medium heat, stirring constantly. Boil 4 to 5 minutes or until mixture starts to thicken.
Remove from heat. Stir in marshmallows, chocolate chips, vanilla and nuts (if desired) until marshmallows and chocolate melt and blend.
Pour into prepared pan. Chill until set.
Cut into 1-inch (2.5 cm) squares. Store in refrigerator in sealed container.
