Prepare an 8×8-inch baking dish for thinner fudge pieces or a 9×5-inch loaf pan for thicker cuts by lightly greasing it with butter or lining with parchment paper; set aside.

Have all ingredients measured and ready before starting, particularly the peanut butter, butter, vanilla, and salt, as timing is crucial once cooking begins.

In a medium saucepan set over medium heat, combine the granulated sugar and evaporated milk. Stir the mixture occasionally to incorporate. Before the mixture reaches a boil, use a damp pastry brush to gently clean the inner sides of the pan, removing any adhering sugar crystals.

Continue stirring periodically until the sugar fully dissolves and the mixture reaches a rolling boil. At this point, affix a candy thermometer to the pot, ensuring the sensor tip is immersed in the center of the mixture without touching the pan's bottom.

Maintain a steady boil, stirring constantly, until the thermometer registers between 234°F and 236°F (112°C to 113°C).

Immediately remove the saucepan from the heat and add the creamy peanut butter, softened butter, vanilla extract, and salt. Stir briskly but gently until the ingredients are fully melted, the fudge is smooth, and it begins to thicken slightly (approximately 1 to 3 minutes). Avoid scraping the pan’s sides during this process.

Pour the mixture directly into the prepared pan without disturbing any residue on the pot’s sides. Allow the fudge to set undisturbed at room temperature for several hours, or accelerate the process by refrigerating.

Once firm, cut the fudge into small squares and serve.