Line a 9x13 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal. Lightly spray the parchment with cooking spray or brush with butter and set aside.
Measure the chocolate chips, marshmallow creme, vanilla, and nuts (if using) into a large mixing bowl and keep it right next to the stove for easy access.
In a heavy-bottomed saucepan, combine the sugar, butter, and evaporated milk. Stir constantly over medium heat until the butter melts and the sugar dissolves completely.
Increase heat to medium-high and bring the mixture to a full rolling boil, stirring constantly to prevent burning and ensure even heating.
Once at a rolling boil, set a timer for exactly 5 minutes and continue stirring constantly. The mixture will become slightly thicker and darker in color.
Immediately remove the saucepan from heat after 5 minutes and pour the hot mixture over the chocolate chips and marshmallow creme in your prepared bowl. Work quickly but carefully as the mixture is extremely hot.
Stir vigorously until all the chocolate chips are completely melted and the marshmallow creme is fully incorporated, about 2-3 minutes. Add the vanilla extract and nuts (if using) and stir until evenly distributed.
Immediately pour the fudge mixture into your prepared pan and use a spatula to spread it evenly into all corners, smoothing the top as much as possible while still warm.
Allow the fudge to cool at room temperature for at least 2 hours, or until completely set and firm to the touch. For faster setting, refrigerate after 30 minutes of room temperature cooling.
Use the parchment paper overhang to lift the fudge out of the pan. Place on a cutting board and cut into squares with a sharp knife, wiping the knife with a damp cloth between each cut for clean edges.