Line a 13x9-inch pan with foil, lightly spray with cooking spray. Set aside.
In a large, microwave safe bowl, add chocolate chips and condensed milk. Microwave for about 40 seconds, or until the chips are just melted when you stir them. If needed, continue to microwave in 15 second increments until melted. Do not overcook. Immediately stir in vanilla and salt. Then fold in the marshmallows and nuts.
Working quickly, spread and press fudge into the prepared pan. Refrigerate until completely cooled before cutting into squares.
