Line an 8x8-inch baking pan with parchment paper, leaving overhang on two opposite sides, and lightly grease the parchment.

Measure the peanut butter, marshmallow creme, vanilla extract, and salt into separate dishes so they are ready to add quickly.

In a medium heavy-bottomed saucepan combine the granulated sugar, whole milk, and unsalted butter over medium heat, stirring constantly until the sugar dissolves and the butter melts, about 2 minutes.

Stop stirring and bring the mixture to a rolling boil. Continue boiling undisturbed for exactly 2 minutes, or until a candy thermometer reads 234-240°F (soft-ball stage).

Immediately remove the pan from the heat.

Quickly stir in the creamy peanut butter and marshmallow creme until the mixture is smooth and uniform with no streaks, about 30 seconds.

Stir in the vanilla extract and salt until fully incorporated.

Pour the hot fudge into the prepared pan and spread it evenly with a spatula.

Let the fudge cool at room temperature until completely set, about 90 minutes, or refrigerate for 45 minutes to speed up the process.

Lift the set fudge out of the pan using the parchment overhang and cut into 36 squares, wiping the knife between cuts for clean edges.