Line 8-inch baking dish with foil or parchment paper; lightly grease and set aside.
In a heavy-duty sauce pan, combine sugar, evaporated milk, butter and salt. Bring to a boil, stirring often; continue to boil and stir for 4-5 minutes.
Remove from heat and add marshmallows, chocolate morsels and vanilla. Beat vigorously for 1 minute or until marshmallows are melted.
Pour into prepared pan and use a lightly greased spatula to spread mixture into corners of the pan.
Let fudge cool to room temperature and refrigerate for 2 hours before cutting into squares. Store in an airtight container