3 cups packed light brown sugar (light brown sugar works better than dark brown sugar for this recipe)
1 cup heavy cream
2 Tbsp unsalted butter
1 tsp vanilla extract
1/4 tsp salt
Line a 9-inch square baking pan with foil, leaving overhang on all sides. Grease the foil. Combine all the ingredients in a medium saucepan and bring to boil over medium- high heat. Reduce the heat to medium-low and cook until the mixture reaches the soft-ball stage on a candy thermometer, about 234 degrees, 5-8 minutes.
Remove the pan from the heat and allow to cool until just warm (about 120 degrees) and not yet firm, 35-45 minutes. Using a wooden spoon, stir vigorously until the mixture lightens and is no longer shiny, 6-10 minutes. Spread the mixture into the prepared pan and let sit until firm, about 1 hour. Using the foil overhang, remove the fudge from the pan and cut into 1-inch squares. (The fudge can be stored in an airtight container for up to 1 month.)
For another option: Try adding 1/2 cup chopped hazelnuts or pecans, which will make the fudge taste like praline.