Begin by greasing a 9x13-inch baking dish with butter or cooking spray. Alternatively, line with parchment paper for easier removal.
In a large, heavy-bottomed saucepan, combine sugar and evaporated milk. Bring to a rolling boil over medium heat, stirring constantly to prevent scorching.
Once boiling, continue to cook for exactly 5 minutes while stirring continuously. Timing is crucial for perfect texture!
Remove from heat and quickly stir in butter until melted.
Add peanut butter, stirring vigorously until completely incorporated and smooth.
Fold in the marshmallow cream and vanilla extract, mixing until fully blended and no white streaks remain.
Working quickly, pour the fudge mixture into your prepared baking dish and spread into an even layer.
Allow to cool completely at room temperature until set, approximately 2-3 hours.
Once set, cut into small squares and enjoy.