In a large, heavy pan over medium heat, mix together sugar and evaporated milk. Bring to a boil stirring frequently to keep mixture from burning.
After mixture comes to a boil, cook for five minutes, stirring occasionally.
Meanwhile, break up the chocolate bar into a large bowl and add chocolate chips.
Remove milk and sugar mixture from heat and add chocolate. Stir until smooth and thoroughly combined.
Add marshmallow, vanilla, and dash of salt; mix well to combine.*
Pour onto waxed paper, roll to form logs, and refrigerate until set.
Notes
If you want the whole batch with nuts or peanut butter, you can add them at the same time as the marshmallow crème.
If you'd like to get a variety from one batch, I divide the candy into thirds by using small pans. First, using a food scale, I pour about one pound of fudge into a small, well-buttered loaf pan and set aside. I then add some nuts to two small buttered loaf pans, pour about a pound of fudge into each pan, and then stir to distribute the nuts. Finally, I add some peanut butter to what remains in the pan, stir lightly to distribute, but leave ribbons of peanut butter, and pour that into a well-buttered 8 x 8 dish.