Line an 8-inch square baking dish with parchment paper.
In a medium saucepan, combine chocolate chips, sweetened condensed milk, and butter.
Heat over low heat, stirring constantly until melted and smooth.
Remove from heat and stir in vanilla extract and salt.
If desired, fold in nuts or sprinkles.
Pour the chocolate mixture into the prepared baking dish.
Spread evenly with a spatula.
Refrigerate for at least 2 hours or until firm.
Once set, lift the fudge from the dish using the parchment paper.
Cut into squares and enjoy!