Butter an 8×8-inch baking dish or spray it with nonstick cooking spray and set aside.
Combine the sugar, milk, and butter in a medium sized pot and cook on medium-low heat until the mixture comes to a boil. Be sure to stir frequently.
Once it has reached the boiling point, boil for 5 minutes. Stir constantly. Seriously. Constantly. The mixture can scorch and you don't want that. You can even adjust the heat down some to maintain a boil without it scorching. The goal here is to get the mixture to the soft ball temp of 235°F. Having a candy thermometer is a bit of an insurance policy, but it's not required if you cook it per the instructions.
Remove from the heat and stir in the chocolate chips until the mixture is smooth.
Put your marshmallow creme in the microwave for about 10-15 seconds (no lid! no bits of foil! Ignore the “do not microwave this container” warning!) Watch it and take it out when the mallow rises about a bit over the lip of the container.
Add the marshmallow creme and vanilla to the mixture and stir until it is creamy and smooth.
Fold in the chopped nuts (reserving a few to sprinkle on the top) and mix well.
Pour into the prepared baking dish.
Cool completely and cut as desired.