Prepare the Pan: Line a 9x9-inch baking dish with parchment paper or lightly grease it with butter to prevent sticking.
Melt Sugar and Butter: In a heavy-bottomed saucepan, combine the brown sugar, butter, and salt. Stir constantly over medium heat until the butter is melted and the sugar starts to dissolve.
Add Condensed Milk: Slowly add the sweetened condensed milk to the mixture, stirring as you go. Continue to cook and bring the mixture to a gentle boil, being careful not to let it burn.
Simmer and Stir: Let the mixture simmer for 10-15 minutes while stirring constantly. You should notice it thickening into a rich, caramel-like consistency.
Add Flavorings: Once the fudge has thickened, remove the pan from the heat. Stir in the vanilla extract and any optional add-ins like chopped nuts or shredded coconut.
Set the Fudge: Pour the mixture into the prepared baking dish. Smooth it out evenly and let it cool to room temperature. Afterward, refrigerate it for 2-3 hours, or until fully set.
Cut and Serve: Once set, cut the fudge into small squares and serve!
