In a medium saucepan, combine white sugar, evaporated milk, butter, and salt over medium heat. Stir constantly and bring to a rolling boil. Cook for 3-4 minutes while stirring.
Remove from heat and stir in milk chocolate chips and marshmallows until melted and smooth.
Mix in vanilla extract and chopped nuts, stirring to combine evenly.
Pour the mixture into a greased 8x8-inch baking dish, spreading it evenly.
Let the fudge cool at room temperature until firm or refrigerate for faster setting. Cut into squares and enjoy!
Notes
For a softer texture, use mini marshmallows instead of large ones. Store at room temperature for up to a week or freeze for up to 3 months.