Line a 9×13-inch baking pan with parchment paper, making sure there is some overhang on the sides for easy removal. Set aside.

In a large, heavy-bottomed saucepan, combine granulated sugar, unsalted butter, and evaporated milk. Place over medium heat and cook, stirring constantly with a wooden spoon or heatproof silicone spatula.

Bring the mixture to a boil. Continue stirring while boiling until the mixture reaches 234°F on a candy thermometer. This should take about 5 minutes.

Remove the saucepan from the heat. Immediately stir in the creamy peanut butter until fully melted and smooth.

Add the marshmallow fluff and vanilla extract. Stir vigorously until everything is well combined and the mixture is smooth and glossy.

Pour the fudge into the prepared pan. Use an offset spatula or the back of a spoon to smooth the top.

Let the fudge cool at room temperature for about 2 hours, or until fully set. Once firm, lift the fudge out using the parchment overhang and cut into squares.