Line a 9x9 inch baking dish with parchment paper, leaving overhang for easy removal.

In a medium saucepan, combine granulated sugar, unsalted butter, and evaporated milk over medium heat.

Stir the mixture constantly and bring to a boil.

Once boiling, continue to boil for 5 minutes, stirring constantly to prevent burning.

Remove the saucepan from heat and stir in the semi-sweet chocolate chips until fully melted.

Add the marshmallow fluff and vanilla extract to the chocolate mixture and stir until smooth.

Fold in the chopped nuts, if using, until evenly distributed.

Pour the fudge mixture into the prepared baking dish and spread evenly with a spatula.

Refrigerate the fudge for at least 2 hours to set before cutting into squares.