Line a 13x9 inch baking dish with parchment paper OR grease with cooking spray.
Place evaporated milk, sugar, and salt in a large saucepan. Bring to a boil over medium heat, and cook until mixture reaches 235°F on a candy thermometer, about 8–12 minutes.
Remove from the heat and stir in the peanut butter and marshmallow creme until completely smooth. Pour into the prepared pan.
Allow to cool completely before cutting into 1-inch squares. It will take about 4 hours at room temperature or 2 hours in the refrigerator.
Notes
Tips for getting clean cuts: run a sharp knife under hot water, then wipe clean with a kitchen towel. Slice the fudge, repeating the process as necessary when the knife gets dirty. Storage: if you like a softer fudge, keep it at room temperature. If you prefer a more firm fudge, store it in the refrigerator. Either way, keep it in a covered dish and place pieces of wax paper or parchment paper in between layers to prevent sticking. Freezing: the fudge can be frozen for up to 3 months.