Use nonstick cooking spray to lightly grease a 5x9-inch loaf pan.
Line it with plastic wrap or parchment paper.
Stir the brown sugar and butter together in a heavy pot over a moderately low heat until the sugar dissolves and the butter melts.
Add the evaporated milk and bring the fudge mixture to a boil.
Take it off the heat and let it cool down for half an hour.
Stir in the vanilla and salt.
Beat in the powdered sugar, bit by bit.
Fold in the nuts, then spoon the mixture into the prepared loaf tin.
Refrigerate for 20 minutes, not covered.
Once the fudge is set, you can cut it into pieces and serve.