Here's your first tip, you are going to want to stir the chocolate as it's melting non-stop, otherwise, it'll burn to the bottom of the pan. Prep your 9x9 pan by spraying the pan with non-stick cooking spray, then line it with parchment paper. This will make it much easier to remove from the pan when it's time to slice the fudge. In a medium saucepan combine the sweetened condensed milk, salt, and chocolate. Heat over low heat, continuously stirring it as it melts. Once the chocolate has melted, remove from heat, still in vanilla extract. Pour into your prepped pan and let cool. If you live in a humid or hot climate you may need to place the fudge in the refrigerator to firm up. Once firm, slice in to bite-size pieces and enjoy!