In a medium saucepan over low heat, combine chocolate chips, sweetened condensed milk, and salt. Stir constantly until chocolate is melted and mixture is smooth.
Remove from heat and stir in vanilla extract.
Pour the mixture into a lined and greased 8x8 inch baking dish. Spread evenly.
Refrigerate for 2 hours or until firm. Cut into squares and serve.
Notes
For a festive touch, top the fudge with crushed candy canes before refrigerating.