Prepare an 8″x8” pan by lining it with aluminum foil and spraying the foil with nonstick cooking spray.
In a large microwave-safe bowl, combine the chocolate chips, condensed milk, and butter. Microwave in one-minute increments until melted, about 2–3 minutes. Stir to ensure all the chocolate is melted, then add the vanilla and salt. Stir until the candy is smooth and well-mixed.
Pour the fudge into the prepared pan and smooth it into an even layer.
Place the fudge in the refrigerator to set for at least 2 hours. Once set, cut into 1-inch squares and serve at room temperature.
Notes
Store excess fudge in an airtight container in the refrigerator.