**Prepare the Baking Dish:** Line a 9x13-inch baking dish with parchment paper or aluminum foil, leaving some overhang for easy removal. Set aside.
**Combine Sugar, Milk, and Butter:** In a medium saucepan over medium heat, combine the granulated sugar, evaporated milk, and butter. Stir continuously until the mixture comes to a boil.
**Boil the Mixture:** Once boiling, reduce the heat slightly and let it boil for 7-8 minutes, stirring constantly to prevent burning.
**Add Chocolate and Marshmallow Creme:** Remove the saucepan from the heat and immediately stir in the semisweet chocolate chips, milk chocolate chips, and marshmallow creme. Mix until fully melted and smooth.
**Add Vanilla and Nuts:** Stir in the vanilla extract and chopped nuts (if using).
**Pour Into the Dish:** Quickly pour the fudge mixture into the prepared baking dish, spreading it evenly with a spatula.
**Cool and Set:** Allow the fudge to cool completely at room temperature, then refrigerate for 2-3 hours or until firm.
**Cut and Serve:** Lift the fudge out of the dish using the parchment paper or foil overhang. Cut into squares and serve.